Draft: Add link to latest author in wiki page header

What does this MR do?

This MR adds the user avatar and popover to the wiki page header.

UX notes:

• Styling is slightly different than previously (darker text, slightly different copy). The intention here is to replicate issue/MR headers as closely as possible
• The hover state of the user's name is blue, whereas on issues/MRs, there is no change (remains #303030). This is because we don't have the appropriate classes available in gitlab-ui. I will create follow-up issues/MR's to address this.

Related to #26070 (closed)

Screenshots (strongly suggested)

Before	After

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