Inject namespace header

[Quinn-With-Two-Ns]

Inject Namespace in grpc headers. Unfortunately I couldn't use gRPC interceptors as originally proposed because java's gRPC interceptors cannot modify the header based of the content of the message grpc/grpc-java#4684 (comment)

closes #2058

[cretz]

LGTM. As a separate issue, we should consider a test with cloud data plane and API key to confirm this works there, but I may open some separate issues on that.

[nzuguem]

Since release v1.28.0, I've had a problem (io.grpc.StatusRuntimeException: PERMISSION_DENIED: Request unauthorized) with authentication via API Key to Temporal Cloud. After investigation (via git bisect) I can see that it's this PR that's causing the problem.

I may create a separate issue

[Quinn-With-Two-Ns]

@nzuguem for issues connecting to Temporal cloud please use reach out to support to create a ticket

[nzuguem]

Thanks for your answer. I'm going to create a ticket for Temporal Cloud.

I'd like to remind you that this worked normally with SDK v1.27.1, but since v1.28.0 with the addition of interceptors in this PR, it no longer works. I've even tried removing the interceptors I added manually, but it still doesn't work.