Anonymize GitLab mentions on Status Detail Pages

What does this MR do?

Refs #208993 (closed)

📯 This MR is based on !30181 (merged) hence the WIP. Please don't merge yet.

This MR implements a HTML filter which takes care of anonymizing user, group, and all mentions from issue title, issue description and note content.

We achieve this by replacing any occurrence of a linked GitLab username by Incident Responder. See #208993 (comment 302875437) & &2479 (comment 302808045).

A more sophisticated approach will be taken via #209114 later.

Screenshots

Issue	Status Page

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team