Replace gogo protobuf with google's protobuf v2 compiler (#317)

**What changed?**

gogo/protobuf has been replaced with Google's official go compiler.

I also changed our code generation to use buf as it was slightly easier to manage plugin versions, though I may revert that.

**Why?**

gogo/protobuf has been deprecated for some time and the community is moving on, building new tools (like vtproto) atop google's v2 compiler.

**Breaking changes**

-  in proto structs will now be [timestamppb.Timestamp](https://pkg.go.dev/google.golang.org/[email protected]/types/known/timestamppb#section-documentation)
-  will now be [durationpb.Duration](https://pkg.go.dev/google.golang.org/protobuf/types/known/durationpb)
- V2-generated structs embed locks, so you cannot dereference them willy-nilly.  will scream at you about this
- Proto enums will, when formatted to JSON, now be in  rather than . We decided (in discussion with the SDK team) that now was as good a time as any to rip the bandage off