grpc: configure client keep alive for grpc connections

[famarting]

Is your feature request related to a problem? Please describe.

This feature request would help making the grpc connections to dapr more reliable. I'm suggesting to either configure a default keepalive on the grpc connections or add a config option to enable keepalives.

Specifically thinking of the workflows SDK, the grpc streamed connection would benefit from keepalives. The long lived grpc streamed connections used in workflows is key for the correct function of workflows, so my understanding is that by using keepalives we would make the grpc connection to stay healthy for longer periods of time.

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Additional context

[famarting]

I would create an equivalent issue for other SDKs