Add a link to the homepage to the GitLab logo.

What does this MR do?

Adds links to the homepage on the GitLab logo on the http status code pages (404, 500, etc.)

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

Nope

Why was this MR needed?

I have two GitLab accounts (one personal, one work). If go directly to a private repository on one account while signed into another of the accounts, it's a pain to get to repository. Clicking the "Go Back" link doesn't work because I wasn't previously on GitLab since I just navigated directly there. This MR lets me (And everyone!) just click on the GitLab logo to go to a page where I can switch to the right account instead of having to go back to the Location bar and type a gitlab link that will actually load in my current signed in account.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?