Tidy-up Authz gRPC service

[uatuko]

Favour entity over resource for protobuf field names.

💡 Since this is just a field name change (and not type or number change) this is a non-breaking change.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.32%. Comparing base (5d41255) to head (ed804fb).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #90 +/- ## ========================================== - Coverage 93.33% 93.32% -0.02% ========================================== Files 20 20 Lines 1245 1243 -2 Branches 123 123 ========================================== - Hits 1162 1160 -2 Misses 67 67 Partials 16 16 ```

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