Replace buf.build dependency or extract protovalidator interceptor

[a-menshchikov]

At the moment buf.build domain is inaccessible from Russia, therefore the whole go-grpc-middleware package is inaccessible for usage because of the buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go dependency too.

It would be very convenient if this dependency will be replaced with some other package or the code from it will be moved into the go-grpc-middleware code. Or if the protovalidator interceptor will be moved into the separated package.

[johanbrandhorst]

Hi, thanks for your bug report. Is it possible to work around this by running a local GOPROXY? I assume you should be able to access the buf.build source once and cache it for future use? Alternatively, you could use a go.mod replace to point at some local code? It would be a bit of a pain to remove this dependency since we'd need to maintain a fork.