Add an opt-out option for the extractIncludeProto/extractIncludeTestProto tasks

Our projects have a mix of proto and java content. The dependency list is quite long because of the java content, but the proto content doesn't actually have any external dependencies.

Right now, the protobuf plugin is a bit sluggish because it wants to scan all dependencies for proto files when we know that there is none to be found.

It would be nice to have a way to turn off that functionnality in the plugin configuration.

Currently we have put in place a workaround to de-activate those tasks but a solution in the plugin would be better.