Draft: Resolve "Add missing markdown examples to Markdown Golden Master spec YAML config"

What does this MR do and why?

Describe in detail what your merge request does and why.

The following discussion from !68671 (merged) should be addressed (see discussion thread):

how is this reconciled with our use of https://gitlab.com/gitlab-org/gitlab/blob/master/spec/fixtures/markdown.md.erb? Is everything in there covered in the new yaml file? Is one generated from the other?

@digitalmoksha I wasn't aware of that, so this Golden Master MR doesn't contain all of those examples. It's currently focused on just replacing the existing Content Editor frontend-fixtures based approach.

However, it's a great idea, and it definitely should have examples added for all markdown elements which the backend currently supports. And, with the pending attribute support, it's easy to add examples to test the backend even if the frontend doesn't support them yet.

Let's make a followup MR to add these to the config file, and discuss whether we should automate some sort of synchronization.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

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

MR 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 MR.

Related to #345548 (closed)