Draft: Replace Gitaly Wiki create page RPC [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This MR replaces the current wiki_create_page RPC.

TODO

• It mustn't be possible to create two pages with the same title (page1.md and page1.rdoc)
• It mustn't be possible to create two pages with different capitalization but same string (If page.md exists we cannot create Page.md or pagE.md).

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content