Configure how to process YAML header / front matter for translation

Issue description from @wojciech.froelich comment here.

• Verify and document the correct settings for processing YAML headers in docs.
• Ensure that YAML headers / front matters are created in translated files without breaking the pipelines
  • The problem is that this content will be segmented and shown to translators at the beginning of the document.
  • This content needs to remain untranslated
• We need to verify what problems this cause with the parser and in which scenarios

Example of a yml header:

https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/user/gitlab_duo/index.md