give the user to be able to change the stub, in the case that he want use a older version of core lightning

[vincenzopalazzo]

older version of core lighting required an older version of the proton file (usually) and we need to allow the user to change the GRPC implementation and use the own implementation

Also, I'm assuming that https://blog.blockstream.com/en-greenlight-by-blockstream-lightning-made-easy/ by blockstre will use the grpc and this can allow a possible user of green light to use these API

We need to think a little bit on it