Enhancement: only include correspondent 'last_correspondence' if requested

[shamoon]

Proposed change

After reading the linked issues, I wondered if the annotation query to pull out 'last_correspondence' is unnecessarily slowing things down. Im not really sure how to test other than asking the users (at least one seems briefly to confirm so far) but I think this would still be an improvement for all users (e.g. faster) and we only use last_correspondence in one place currently (I think), in the list of correspondents, in which case the records are paginated already.

I suppose there's the question of whether this qualifies as a breaking change as getting the value in a list of correspondents would now require passing last_correspondence=true. As always welcome any thoughts in general or of course if I'm missing anything.

Note: the changes to document-detail here are just a side-effect of this, we previously used the presence of last_correspondence on an object to check what type it was, but didnt actually use it there. That is significantly cleaner now anyway.

Closes #6782 (and perhaps relevant to #4872?)

Type of change

• Bug fix: non-breaking change which fixes an issue.
• New feature / Enhancement: non-breaking change which adds functionality. Please read the important note above.
• Breaking change: fix or feature that would cause existing functionality to not work as expected.
• Documentation only.
• Other. Please explain:

Checklist:

• I have read & agree with the contributing guidelines.
• If applicable, I have included testing coverage for new code in this PR, for backend and / or front-end changes.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• If applicable, I have checked that all tests pass, see documentation.
• I have run all pre-commit hooks, see documentation.
• I have made corresponding changes to the documentation as needed.
• I have checked my modifications for any breaking changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.21%. Comparing base (3e62f13) to head (f6b08d5).
Report is 1 commits behind head on dev.

❗ Current head f6b08d5 differs from pull request most recent head ed056dc

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Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #6792   +/-   ##
=======================================
  Coverage   97.21%   97.21%           
=======================================
  Files         438      438           
  Lines       18069    18087   +18     
  Branches     1518     1532   +14     
=======================================
+ Hits        17565    17583   +18     
+ Misses        504      501    -3     
- Partials        0        3    +3     

Flag	Coverage Δ
backend	95.90% <100.00%> (+<0.01%)	⬆️
frontend	98.64% <100.00%> (+<0.01%)	⬆️

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[stumpylog]

I guess it's kind of breaking, but seems pretty minor

[github-actions]

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