There are several main changes in this PR:
Create envoy.api.v2.core packages to break circular dependencies from xDS on to subpackages on to base protos.
Create individual packages for each filter and add independent versioning to each filter.
Add visibility constraints to prevent formation of dependency cycles.
Add gogoproto annotations to improve go code generation.
After moving xDS service definitions and top-level resource protos back to envoy.core.api.v2, cycles were created, since the second-level definitions depend on base protobuf definitions, and are in turn included from xDS; however xDS and base definitions are in the same package.
The solution is to split the base protos into another package, envoy.api.v2.core. That eliminates dependency cycles (validated using go-control-plane).
Added a few gogoproto annotations to improve golang code generation.
Signed-off-by: Kuat Yessenov <kuat@google.com>
Kuat