[Feature Request] Move/remove third party protos to a separate place instead of root

Describe the solution you'd like

Other users protoc from the root of this repo. When https://github.com/temporalio/api/commit/108b40ae508505b64f19ccbe2fdbcd304081391b was done, we put google-based proto dependencies at the same path as our own assuming that all users were ok with using these google protos instead of their own (e.g. from https://github.com/protocolbuffers/protobuf/tree/main/src/google/protobuf).

We probably need to either:

• Put the third party references where the protoc is actually run (e.g. api-go) and only embed them here when testing

or:

• Move google/api to thirdparty/google-api/google/api
• Move google/protobuf to thirdparty/google-protobuf/google/protobuf
• Add -I thirdparty/google-api and -I thirdparty/google-protobuf to our protoc
• Confirm the fact that thirdparty is nested under our root is ok and can easily be ignored by most protoc use

Inspect the current root-level google/api and google/protobuf paths and find where protoc is invoked in api-go. Compare the proposed relocation and include-path changes, then verify that repository protoc commands still work while external users can use their own third-party protos.