Cloudstate protobuf files define an incorrect and incompatible "go_package"

[marcellanz]

All Cloudstate .protobuf files define an incorrect and incompatible go_package:
https://github.com/cloudstateio/cloudstate/blob/v0.5.1/protocols/protocol/cloudstate/event_sourced.proto#L27

option go_package = "cloudstate/protocol";

While this works to some extent, some tools don't like the incorrect use of such a go package, one is CUE.
The protocol buffers reference documentation defines:

The .proto file should contain a go_package option specifying the full import path of the Go package that contains the generated code.

which leads to the following correct definition:

option go_package = "github.com/cloudstateio/go-support/cloudstate/protocol;protocol";

The Go User Language Support Library with milestone v0.2.x corrects this. Changes have to be copied over to the main repository.

[pvlugter]

@marcellanz, sounds good to just go ahead and apply these changes to the cloudstate repo.