Add backticks and remove brackets causing kramdown warnings

What does this MR do?

Add backticks and remove brackets as needed to fix kramdown warnings:

kramdown warning(s) for <Nanoc::CompilationItemRepView item.identifier=/ce/api/projects.md name=default>
  No link definition for link ID 'int' found on line 1
kramdown warning(s) for <Nanoc::CompilationItemRepView item.identifier=/ce/administration/issue_closing_pattern.md name=default>
  No link definition for link ID '`gitlab.yml.example`' found on line 19
kramdown warning(s) for <Nanoc::CompilationItemRepView item.identifier=/ce/administration/monitoring/prometheus/gitlab_metrics.md name=default>
  Found no end tag for 'key' (line 102) - auto-closing it
  Found no end tag for 'key' (line 101) - auto-closing it
  Found no end tag for 'key' (line 1) - auto-closing it
  Found no end tag for 'key' (line 1) - auto-closing it

Related issues

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the ~Documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set and that you merge the equivalent EE MR before the CE MR if both exist.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.