The `BoardListWatch` process must not be stopped when installing/uninstalling/upgrading a core or library

[silvanocerza]

Bug Report

Current behavior

The BoardListWatch process is stopped each time a client calls the Init directly or indirectly from another gRPC function.
This makes it hard for gRPC clients to handle the BoardListWatch process.

Expected behavior

The BoardListWatch process never stops after is started by a gRPC client, but handles gracefully and transparently the Initialization of the CLI internal Instance.

Environment

• CLI version (output of arduino-cli version): 0.20.2
• OS and platform: Any

Additional context

This is related to #1587, #1460, and arduino/arduino-ide#674.

The arduino/arduino-ide#674 is a fast workaround to handle #1587 and another issue only reported by @ubidefeo that stops the discovery processes on the IDE even though the quit event mentioned in #1587 is sent correctly.

When this issue will be fixed we can remove the arduino/arduino-ide#674 workaround.