respect offset and limit query params for infinite lists

What does this MR do?

For lists using Pager: use "offset" query param if it exists. And ignore it in subsequent requests.

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

• init param order - should callback be last, or use an object for named params

Why was this MR needed?

If offset is included in the URL of a page that uses an infinite list (using Pager.js), they get ignored for ajax requests.

This MR initialises offset from the URL, and ensures we don't send duplicate offset values in later requests

Screenshots (if relevant)

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?

Fixes #28030 (closed)