Validate protos workflow

[cody-littley]

Why are these changes needed?

Supersedes #787 I still think it's ugly to commit compiled protobuf files, but I can understand the argument that removing them presents short term risks that could be disruptive.

This PR adds a new CI check that will fail if there are .proto changes without the compiled .proto.go files being properly checked in.

I have verified that this check passes when there are no spurious protobuf changes, and fails when I modify a protobuf file without committing the compiled files. This new job runs in parallel with the others and completes in less than a minute, so it shouldn't have any impact on the end-to-end time for checks to pass.

Checks

• I've made sure the lint is passing in this PR.
• I've made sure the tests are passing. Note that there might be a few flaky tests, in that case, please comment that they are not relevant.
• I've checked the new test coverage and the coverage percentage didn't drop.
• Testing Strategy
  • Unit tests
  • Integration tests
  • This PR is not tested :(