Add Endpoints For Project Items

[JoannaaKL]

Second batch of work to cover new Projects V2 API.
Covers all endpoints for project items : https://docs.github.com/en/rest/projects/items?apiVersion=2022-11-28

FYI I based this work on the earlier pr #3718

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.18%. Comparing base (5cf155c) to head (0c5356d).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
github/projects.go	96.85%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3733      +/-   ##
==========================================
+ Coverage   91.11%   91.18%   +0.06%     
==========================================
  Files         187      188       +1     
  Lines       16686    16878     +192     
==========================================
+ Hits        15204    15390     +186     
- Misses       1295     1299       +4     
- Partials      187      189       +2     

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[gmlewis]

@JoannaaKL - while we are waiting on the other PR (which this one appears to include and will hopefully be rectified after the other is merged) - can you please investigate the poor codecov checks? It could be that not all test functions have been written. Thank you!