The version of Protocol Buffers in the Docker file is too old

[upbqdn]

The implementation of the new gRPC endpoint contains a proto3 type definition with an optional field. Support for optional fields was enabled by default in Protocol Buffers v3.15.0: https://github.com/protocolbuffers/protobuf/releases/tag/v3.15.0. However, our Docker file uses Debian Bullseye with the protobuf-compiler package containing Protocol Buffers v3.12: https://packages.debian.org/bullseye/protobuf-compiler, which doesn't support optional fields by default.