Replace various //go:generate lines and regenerate.sh scripts with a
single, top-level regenerate.sh that regenerates all .pb.go files.
Placing generation in a single script ensures that all files are
generated with similar parameters. The new regenerate.sh uses the
protoc-gen-go version defined in test/tools/go.mod and automatically
handles new .proto files as they are added.
Do some minor refactoring on .proto files: Every file now has a
go_package option (which will be required by a future version of the
code generator), and file imports are all relative to the repository
root.
Method logger will be picked by each RPC at the beginning to log binary entries. It also handles truncating.
This PR also adds script to download proto from grpc/grpc-proto
