Changed the Caching of User Avatars to be public and to 5 minutes

What does this MR do?

It changes the caching of user avatars and Appearances (Custom Logos) to 5 minutes and public caching. This should improve performance when loading and rendering. Also we can leverage with this auomatic image resizing through the CDN.

Before

Cache-Control: private, max-age=0

After

Cache-Control: max-age=300, public

What are the relevant issue numbers?

#51126 (moved)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer