Eliminate `BoardListWatchRequest#interrupt` from the gRPC API, make it server-streaming only

[kittaakos]

Describe the request

Starting the gRPC equivalent of the board list watch requires CLI consumers to create a bidirectional stream. The only reason for this API is to support canceling the watch operation from the client. It should be sufficient to cancel the watch command by canceling the request via an abort signal.

Please make the following changes to provide a better API:

• Get rid of BoardListWatchRequest#interrupt.
• Provide a server-streaming API: rpc BoardListWatch(BoardListWatchRequest) returns (stream BoardListWatchResponse) instead of the current one.

Thank you!

Describe the current behavior

See the description how it works now.

Arduino CLI version

0.34.0

Operating system

macOS

Operating system version

13.5

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the nightly build
• My request contains all necessary details