Use IsaacSearchInstructionBuilder for events search endpoints

[axlewin]

Causes "nofilter" events to be hidden from non-staff users.

Also requires frontend and test content updates (the latter to fix the test that's failing on this branch).

[jsharkey13]

A lot of the logic added to the EventsFacade doesn't really belong in a Facade class.

I think part of the problem is there's no good example of how to do this right, at present. Throwing more methods into the GitContentManager has been used before, but isn't right either.

I think that we should make a new Manager class, EventsManager (with the other event-related managers in isaac.api.managers) to hold the business logic, and leave the Facade to do auth/caching and coercion of user-provided params into our Enums.
For that to work, I think the GCM needs a new method to provide a new IsaacSearchInstructionBuilder initialised with the default arguments (make nofilter content hidden by default here, and add a new method to ISIB like searchFor like includeHiddenContent(boolean) and I think avoid using nofilter on the public method name so we can finally move away from the silly tag). You can then customise this in the EventsManager without needing all the properties to be configured in multiple places.

Start by moving the logic for just the three methods you've refactored here down to a manager; don't worry about the rest for now. It may be that three methods in the manager, one per Facace method, is fine. But you may find some repeated logic can be grouped up into private manager methods too!

[codecov]

Codecov Report

❌ Patch coverage is 24.01747% with 174 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.95%. Comparing base (aba8cbf) to head (8c55244).
⚠️ Report is 34 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/cam/cl/dtg/isaac/api/managers/EventsManager.java	14.66%	118 Missing and 10 partials ⚠️
.../java/uk/ac/cam/cl/dtg/isaac/api/EventsFacade.java	28.57%	34 Missing and 1 partial ⚠️
...tg/segue/search/IsaacSearchInstructionBuilder.java	35.71%	6 Missing and 3 partials ⚠️
...am/cl/dtg/segue/dao/content/GitContentManager.java	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #756      +/-   ##
==========================================
+ Coverage   39.92%   39.95%   +0.02%     
==========================================
  Files         545      546       +1     
  Lines       23892    23887       -5     
  Branches     2873     2873              
==========================================
+ Hits         9538     9543       +5     
+ Misses      13444    13436       -8     
+ Partials      910      908       -2     

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