[Feature Request] Ensure gRPC binary metadata headers are supported in C bridge

[cretz]

Describe the solution you'd like

See temporalio/features#671. Probably only have to update C bridge to send different tonic headers if key is suffixed with -bin. But using binary means users may want \n in the body which we don't support today, unsure if we want to handle that now or maybe even require users base64 -bin-suffixed key values it before it reaches us.