WIP: Support rich references

What does this MR do?

This MR implements #23177 (moved). Adds support for rich references in the Banzai filter pipeline. Appending "+" characters to a reference makes the reference "rich" in the sense that extra info is displayed along with the issue number.

This MR adds a data-rich-ref-verbosity attribute on the anchor element which basically measures the number of "+" characters. A post-processing filter then formats the anchor element text accordingly.

Are there points in the code the reviewer needs to double check?

This is still a work in progress. A lot of tests are broken, documentation is missing and functionality is partially implemented.

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#23177 (moved)

Closes #23177 (moved)