Implement custom compilation rules

What does this MR do and why?

Adds handling for files we do not want to publish to the website, or process in our migration scripts.

Warnings from these pages (e.g invalid YAML) are not actionable, so let's keep them out of our logs in order to more easily spot actionable issues.

Screenshots, screen recordings, or links to review app

Migration scripts:

• Before: Pipeline job warns about YAML on pages like gitlab-operator/doc/adr/0003-use-operator-sdk.md https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/6597824202#L125
• After: Warnings from that section are ignored: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/6597960876#L124

Hugo build no longer includes the non-docs docs:

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/blob/main/doc/setup.md.
2. Visit a page that is now ignored, like:

• http://localhost:1313/drawers/advanced_search_syntax/
• http://localhost:1313/operator/adr/0004-integration-of-the-gitlab-chart/

These should now return a 404.

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.

Closes #24 (closed)