Use `page` query parameter instead of `p` to keep consistency with all URLs

What does this MR do?

Uses page in the URL instead of p to keep consistency with all the URLs in gitlab.com and with the enpoint. Added tests to make sure nothing breaks.

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #28248 (closed)