GitLab

* [skip changelog] Add documentation for library components of the gRPC interface

Comments added to the .proto files are included in the generated gRPC interface documentation.

* Correct documentation re: relative vs absolute paths provided by Library message fields
Co-authored-by: Roberto Sora <r.sora@arduino.cc>

* Use preferred "platform" term in gRPC interface documentation

The official term is now "platform", rather than the previous ambiguous "core".
Co-authored-by: Roberto Sora <r.sora@arduino.cc>

* Fix formatting of gRPC interface documentation

* Fix incorrect documentation for task_progress field of LibraryUninstall response

* Document that library version is the key of the releases map

* Update gRPC interface code comments
Co-authored-by: Roberto Sora <r.sora@arduino.cc>