Add `user-agent` property to gRPC client

[cmaglie]

Is your feature request related to a problem? Please describe.
This feature request is related to this new feature of the arduno-cli: arduino/arduino-cli#1640
arduino-cli now passes a new ARDUINO_USER_AGENT env variable to all the tools used to compile and upload. In particular, while running as a daemon arduino-cli will pass also the name of the client using the daemon instance (in our case it will be ArduinoIDE), for example:

ARDUINO_USER_AGENT=arduino-cli/0.21.0 ArduinoIDE/2.0.0-rc3

Describe the solution you'd like
Since gRPC already supports passing the user-agent, I'd like this option to be set to ArduinoIDE/<version>, like ArudinoIDE/2.0.0-rc3

[PaulStoffregen]

@silvanocerza - Any chance to have the IDE send this info soon, now that CLI 0.21 is integrated? I need this info to begin testing on Teensy's upload tool to adapt between GUI vs CLI usage.

[silvanocerza]

@PaulStoffregen I've opened a PR, you should be able to test it as soon as the workflows generate the build artifacts if you don't want to wait for it to be merged in main.

It's a small change so I would expect it will be merged in a short time.