Update protobuf-java to 4.x or 5.x

We are currently at 3.x.

https://protobuf.dev/support/version-support/#java

Check which version we can update to, as this needs to be in sync with other third-party dependencies.

Also, we might have to recompile our generated protobuf classes, which we use for journal messages. With the protobuf compiler making its way into our build process with #21536, we should also consider compiling the protobuf stubs on-demand instead of checking them in.