proto: remove the usage of jsontag

[fdymylja]

In the protofiles of the sdk, we frequently use the gogoproto jsontag option, this should be removed as it breaks the jsonpb specification (proto fields have their own json name).

This becomes particularly important as the jsonpb package gives us free proto to json transcoding.

Doing this change, would allow us to generate the required transcoding at runtime without the usage of the grpc-gateway.

[aaronc]

I don't think this is really api-breaking, maybe...

[fdymylja]

I don't think this is really api-breaking, maybe...

I think something on the grpc-gateway proxy would end up being broken, unless the jsontags perfectly match the pb json names...

[tac0turtle]

can we use json_name instead https://developers.google.com/protocol-buffers/docs/proto3#json?

[tac0turtle]

@fdymylja should we see about including this in 0.45?

[aaronc]

I think any usages of jsontag should go ASAP