🌟feat(responseTrailers): support for response header trailers added

[keblodev]

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• plus GRPC_HEADER_METADATA_KEY_ID to config Grpc-Metadata headers key

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WHAT

Update allowing to receive back headers from the grpc call processing result. plus ability to specify Grpc-Metadata- header key for incoming headers using an environment variable instead of constant value. plus small updates to names as it was confusing to read the code a bit.

WHY

While translation is working great which is awesome! But the biggest issue for us when we were assessing the concept with your repo was the fact that we were not receiving any headers back from the rpc call result. Obviously the header trailers should be returned back to the caller, as they might contain new/updated data that client requires back.

[keblodev]

will update the tests over the weekend