Allow using user bookmarks list as question source

[jacbn]

In doing so, reworks the ID field in the /questions endpoint.

• The list of question IDs to search from has been removed as a parameter (it was entirely unused beforehand, except in the ITs).
• A new bookmarks?: boolean param has been added, which repurposes the functionality of the old ID param to send to ES a list of content IDs – namely those that have been bookmarked – to search within. This allows us to reuse the filtering logic we have for other uses of the /questions endpoint inside a bookmarks search.

The test that is entirely commented out I was not sure what to do with – perhaps we can repurpose it, but given that it requires specifically the list functionality of the old ID param which has no equivalent any longer, perhaps we can also just remove it.

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.28%. Comparing base (de91a63) to head (f1cf09e).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...n/java/uk/ac/cam/cl/dtg/isaac/api/PagesFacade.java	86.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #799      +/-   ##
==========================================
+ Coverage   40.27%   40.28%   +0.01%     
==========================================
  Files         547      547              
  Lines       23806    23814       +8     
  Branches     2896     2898       +2     
==========================================
+ Hits         9587     9593       +6     
- Misses      13317    13320       +3     
+ Partials      902      901       -1     

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[axlewin]

LGTM 👍

R.E. the test that was commented out: I've made some minor changes to repurpose it to test the searchBookmarks param instead. If you're happy with that, this can be merged.

[jacbn]

Amazing, thank you!!