Cleanup protos

[uatuko]

This is mainly to drop google.api.http annotations used for gRPC/JSON transcoding support (9136c98) and to avoid sharing top-level request/response messages across rpcs (29331e3).

gRPC/JSON transcoding support is dropped since Ruek is not expected to be public facing API so there's shouldn't be a need to receive HTTP requests (e.g. from a browser).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.90%. Comparing base (31d51d3) to head (29331e3).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   93.88%   93.90%   +0.02%     
==========================================
  Files          21       21              
  Lines        1406     1411       +5     
  Branches      168      168              
==========================================
+ Hits         1320     1325       +5     
  Misses         59       59              
  Partials       27       27              

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