Verify server sends grpc-accept-encoding appropriately

If the client sends a gzip-encoded request and the server responds with headers (endStream=false) that does not include grpc-accept-encoding gzip, then the client should warn. This is misbehavior on the server-side and would ideally be detected.

Although I said "warn" above, we're actually aware of servers failing to do this properly today. So initially we can use FINE and eventually swap it to warn.

No file, test, or entry point is named. Start by tracing server response-header handling for gzip-encoded requests where endStream=false, then find existing logging and coverage around grpc-accept-encoding. Done means the client detects a missing gzip value and emits a FINE message for this server misbehavior.

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