Proposal: remove dependency on deprecated gogo/protobuf

[krajorama]

Remove dependency on https://github.com/gogo/protobuf .

This would be a breaking change, thus requires a major version bump.

[bboreham]

The reason for picking gogo/protobuf was performance: I would like to be confident that we are moving to one with equal or better performance.

(It shouldn't be a massive ask for httpgrpc which is essentially transporting one string, but still)