Update docs site docs

Review and update all documentation related to the website and tooling.

Required for launch

These should merge before launch:

• Create a brief reference document to outline all the contributor-facing changes that are coming from this project (e.g, title in front matter, shortcodes, index file naming, creating a release, monthly chores, etc) (merged: gitlab-org/gitlab!178338 (merged))
• release process (merged)

We need to merge these as soon as the new site is live, as part of the launch process:

• Contributor docs: https://new.docs.gitlab.com/development/documentation/ and all sub-pages (draft, ready: gitlab-org/gitlab!176057 (merged))
• Docs site self-hosting docs. Will need to update registry paths once project has moved. (draft, ready: gitlab-org/gitlab!179765 (merged))

Can happen shortly after launch

These updates can happen later (but ideally within a week or so of launch).

• Infra service catalog entry (in review: gitlab-com/runbooks!8425 (merged))
• Issue templates: TW onboarding and other team processes (team-tasks!318 (merged))
• Crosslinks from handbook: gitlab-com/content-sites/handbook!11852 (closed)
• Technical docs in this project's doc directory (draft: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/merge_requests/303)
• Project files: LICENSE (done), CONTRIBUTING.md (done), CODEOWNERS (done), README.md
• README.md in gitlab-docs to note new project location