Fix bug with Wiki pages encoding

What does this MR do?

When we retrieve wiki pages from Gitaly they all have a binary encoding. Then we try to decode them to the proper encoding using CharlockHolmes. Sometimes this process brings false negatives, and strings that are indeed UTF8 encoded, results in binary encoded ones.

Also, before this MR, the content of the pages was converted to the matching encoding. But, when the wiki project has a web hook attached, the content is stored into Sidekiq. Because Sidekiq only accepts UTF8 encoding, this process may raise an error.

Why was this MR needed?

To resolve some errors with the wiki page content encoding.

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?

Closes #49512 (closed)