feat(generator): support request_id-like fields

[coryan]

With this change the generator populates the request_id-like fields
and also uses the field to determine if a request is idempotent.

Fixes #13595

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This change is 

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (52b00ee) 93.25% compared to head (fedfab9) 93.25%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
generator/internal/connection_impl_generator.cc	30.00%	7 Missing ⚠️
generator/internal/idempotency_policy_generator.cc	0.00%	6 Missing ⚠️
...ion_tests/tests/request_id_connection_impl_test.cc	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13615      +/-   ##
==========================================
- Coverage   93.25%   93.25%   -0.01%     
==========================================
  Files        2223     2223              
  Lines      193242   193281      +39     
==========================================
+ Hits       180210   180244      +34     
- Misses      13032    13037       +5     

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[scotthart]

Reviewed 6 of 6 files at r1, 4 of 4 files at r2, 3 of 3 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @coryan)