jsonPB is not supporting in grpc gateway v2 migration

[likhita809]

🐛 Bug Report

While migrating to grpc gateway v2 in cosmos sdk, I found that v2 is not supporting JSONPb

Expected behavior

Migration to grpc gateway v2

Actual Behavior

JSONPb is not supporting

[johanbrandhorst]

Hi @likhita809. The Go protobuf APIv2 has a new JSON marshaller package that you need to use. You can find it here: https://pkg.go.dev/google.golang.org/protobuf@v1.25.0/encoding/protojson. If this is unclear in our documentation, I'd be happy to review a submission that makes this clear.