Resolve "Wiki uploaded files are missing"

What does this MR do?

Repairs links to uploads in wiki pages

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

Why was this MR needed?

In the WikiPipeline, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15751 moved the parsing of /uploads/ links from before the WikiLinkFilter to after it. This caused links to uploaded files to be treated as links to wiki contents instead, breaking existing content.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #42031 (closed)