Update the exceptions returned from overdrive API (PP-2154)

[jonathangreen]

Description

Some minor updates to the Overdrive API based on the investigation I'm doing in PP-2154.

• If a book is already on hold return the AlreadyOnHold exception instead of returning a hold info object.
• If a book is checked out when we go to make a loan, don't do an availability sync, just raise NoAvailableCopies.

In both these cases the Circulation API that calls the Overdrive API was doing the same work that was being done in the Overdrive API, so we should just do the simple thing, and let the caller handle the outcome.

I'll add some context in comments on the PR.

Motivation and Context

These don't fix the holds issue in PP-2154, but I think they are good changes to make anyway, having followed through some full OD requests in the debugger.

How Has This Been Tested?

• Running unit tests
• Locally testing with OD loans and holds

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.18%. Comparing base (56cbc4a) to head (2d162e4).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2300      +/-   ##
==========================================
+ Coverage   91.13%   91.18%   +0.05%     
==========================================
  Files         362      362              
  Lines       41361    41358       -3     
  Branches     8863     8863              
==========================================
+ Hits        37693    37711      +18     
+ Misses       2404     2383      -21     
  Partials     1264     1264              

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[dbernstein]

Looks good!