Update dev docs based on markdownlint errors (2/3)

If we want to turn on markdownlint linting in this project, we'll have to clear out the errors it found first.

This MR addresses all the docs in doc/developer:

developer/ci.md:62:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ oc scale --replicas=0 machin..."]
developer/ci.md:110:25 MD044/proper-names Proper names should have the correct capitalization [Expected: YAML; Actual: yaml]
developer/ci.md:157:26 MD044/proper-names Proper names should have the correct capitalization [Expected: GitLab; Actual: gitlab]
developer/ci.md:164 MD024/no-duplicate-heading/no-duplicate-header Multiple headings with the same content [Context: "## Configuration"]
developer/ci.md:171:25 MD044/proper-names Proper names should have the correct capitalization [Expected: YAML; Actual: yaml]
developer/guide.md:12:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ go version"]
developer/guide.md:15:1 MD029/ol-prefix Ordered list item prefix [Expected: 1; Actual: 2; Style: 1/1/1]
developer/guide.md:20:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ operator-sdk version`"]
developer/guide.md:23:38 MD044/proper-names Proper names should have the correct capitalization [Expected: GitLab Operator; Actual: GitLab operator]
developer/guide.md:25:1 MD029/ol-prefix Ordered list item prefix [Expected: 1; Actual: 3; Style: 1/1/1]
developer/guide.md:28:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ git clone git@gitlab.com:git..."]
developer/guide.md:33:5 MD044/proper-names Proper names should have the correct capitalization [Expected: GitLab Operator; Actual: GitLab operator]
developer/guide.md:35 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
developer/guide.md:76:1 MD004/ul-style Unordered list style [Expected: dash; Actual: asterisk]
developer/guide.md:76:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 2]
developer/guide.md:77:1 MD004/ul-style Unordered list style [Expected: dash; Actual: asterisk]
developer/guide.md:77:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 2]
developer/guide.md:79:1 MD004/ul-style Unordered list style [Expected: dash; Actual: asterisk]
developer/guide.md:79:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 2]
developer/guide.md:80:1 MD004/ul-style Unordered list style [Expected: dash; Actual: asterisk]
developer/guide.md:80:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 2]
developer/guide.md:81:1 MD004/ul-style Unordered list style [Expected: dash; Actual: asterisk]
developer/guide.md:81:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 2]
developer/guide.md:91:1 MD004/ul-style Unordered list style [Expected: dash; Actual: asterisk]
developer/guide.md:91:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 2]
developer/guide.md:95 MD012/no-multiple-blanks Multiple consecutive blank lines [Expected: 1; Actual: 2]
developer/guide.md:98:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 1]
developer/guide.md:100 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "   ```"]
developer/guide.md:101:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make bundle"]
developer/guide.md:104:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 1]
developer/guide.md:106 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "   ```"]
developer/guide.md:107:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make docker-build IMG=quay.i..."]
developer/guide.md:110:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 1]
developer/guide.md:112 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "   ```"]
developer/guide.md:113:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make docker-push IMG=quay.io..."]
developer/guide.md:116:1 MD007/ul-indent Unordered list indentation [Expected: 0; Actual: 1]
developer/guide.md:118 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "   ```"]
developer/guide.md:119:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make run"]
developer/installation.md:3:43 MD044/proper-names Proper names should have the correct capitalization [Expected: GitLab Operator; Actual: GitLab operator]
developer/installation.md:13:14 MD044/proper-names Proper names should have the correct capitalization [Expected: GitLab Operator; Actual: GitLab operator]
developer/installation.md:15 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "    ```"]
developer/installation.md:16:5 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ git clone https://gitlab.com..."]
developer/installation.md:17:5 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ cd gitlab-operator"]
developer/installation.md:20:1 MD029/ol-prefix Ordered list item prefix [Expected: 1; Actual: 2; Style: 1/1/1]
developer/installation.md:23:5 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make build_operator"]
developer/installation.md:28 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "    ```"]
developer/installation.md:38:1 MD029/ol-prefix Ordered list item prefix [Expected: 1; Actual: 3; Style: 1/1/1]
developer/installation.md:50:42 MD044/proper-names Proper names should have the correct capitalization [Expected: YAML; Actual: yaml]
developer/installation.md:52:1 MD029/ol-prefix Ordered list item prefix [Expected: 1; Actual: 4; Style: 1/1/1]
developer/installation.md:78:1 MD029/ol-prefix Ordered list item prefix [Expected: 1; Actual: 5; Style: 1/1/1]
developer/installation.md:81:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ kubectl -n gitlab-system app..."]
developer/installation.md:87:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$  kubectl -n gitlab-system lo..."]
developer/installation.md:93:4 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ kubectl get gitlabs -n gitla..."]
developer/installation.md:103:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make clean"]
developer/installation.md:119 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
developer/installation.md:120:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ kubectl -n gitlab-system del..."]
developer/installation.md:127 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
developer/installation.md:128:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make delete_operator"]
developer/installation.md:135 MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
developer/installation.md:136:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ make uninstall_crds"]
developer/releases.md:6 MD025/single-title/single-h1 Multiple top-level headings in the same document [Context: "# Documentation"]
developer/releases.md:23 MD025/single-title/single-h1 Multiple top-level headings in the same document [Context: "# Red Hat Certification"]

Related to #363 (closed)