tendermint-proto: `grpc` feature lost in Tendermint v0.35 shuffle

[tony-iqlusion]

@tomtau added a grpc feature to the tendermint-proto crate in #1137

However it seem it was lost in the shuffle around Tendermint v0.35.

It's needed to implement gRPC "privval" support, as in #1152.

See also: #1134

[tony-iqlusion]

I opened #1227 which cherry-picks the changes from #1137 onto main with some slight modifications

[tony-iqlusion]

Note: the privval side of things is blocked on tendermint/tendermint#9256

[erwanor]

@tony-iqlusion I opened #1338 which includes the server definitions for the rpc and abci service, but not for privval because it's blocked on #9256. I just realized that I used tonic-build@0.9 instead of tonic-build@0.8 in that PR, I can change that.

My motivation is that we want to add gRPC in tower-abci and unfortunately the privval service is blocked by cometbft upstream.