Make internal gRPC client less strict when decoding

[tjanez]

SUMMARY

Current, the client gRPC protocol is not versioned (#1861) and for example, adding a new field makes the client fail with something like:

grpc: failed to unmarshal the received message cbor: found unknown field at map element index 11

Since we are only using the client gRPC protocol between trusted parties, we could make the CBOR decoding less strict and ignore unknown fields.

ISSUE TYPE

• Feature Idea

[kostko]

Note that this should ONLY apply to the internal gRPC client (e.g. for the oasis-node client gRPC protocol), not to any other uses of gRPC (like storage).

[Yawning]

I am against this as it is not possible to rule out unexpected behavior in the future due to default values in new fields that get added, and the same people that will complain about having to keep the client and core build in-sync will be the loudest to complain to us when something bad does happen.