kas to kas request routing

Closes gitlab-org/gitlab#297658 (closed).

Pre-work:

• !282 (merged)
• !283 (merged)
• !288 (merged)
• !297 (merged)
• !296 (merged)
• !306 (merged)
• !300 (merged)
• !256 (merged) this one was needed to pick up https://github.com/rules-proto-grpc/rules_proto_grpc/pull/98 to update grpc-go plugin for the proto compiler to v1.1.0 to pick up https://github.com/grpc/grpc-go/pull/4035 to make it possible to use generated grpc.ServiceDesc that this version exports. This allowed for a much cleaner API to register a gRPC API endpoint for proxying (see the link below).

First commit is generated files, don't need to look at it.

Please see !255 (merged) for an example of how the new API is used by a server module to register for proxying - single line !255 (diffs).