Ensure gRPC binary metadata keys are supported by clients

[cretz]

Describe the solution you'd like

For RPC metadata, users need to be able to pass -bin keys that are sent as gRPC binary headers. This is already supported in native gRPC libraries like Go/Java, but not most Core SDKs. Today, Core SDKs assume string values as ascii headers and Tonic fails if this is done with a -bin header.

We need to accept bytes as RPC metadata values and need to update code to have Tonic set those as binary headers on the metadata map for -bin keys.

Per-SDK Tickets

• Go - N/A
• Java - N/A
• Core - [Feature Request] Ensure gRPC binary metadata headers are supported in C bridge sdk-core#991
• TypeScript - [Feature Request] Ensure gRPC binary metadata headers are supported sdk-typescript#1778
• Python - [Feature Request] Ensure gRPC binary metadata headers are supported sdk-python#1063
• .NET - [Feature Request] Ensure gRPC binary metadata headers are supported sdk-dotnet#512
• Ruby - [Feature Request] Ensure gRPC binary metadata headers are supported sdk-ruby#329
• PHP - N/A
• Temporal CLI - N/A since it leans on Go