Signed-off-by: Kuat Yessenov <kuat@google.com>

Signed-off-by: Sergii Tkachenko <sergiitk@google.com>

Signed-off-by: Sergii Tkachenko <sergiitk@google.com>

py_proto_library provided by @com_google_protobuf//:protobuf.bzl has been deprecated for a while now:

This is provided for backwards compatibility only. Bazel 5.3 will
introduce support for py_proto_library, which should be used instead.
https://github.com/protocolbuffers/protobuf/blob/32af7d211b85f71920acdfa9b796db008f8c2a45/protobuf.bzl#L642-L644

However, native py_proto_library has never been provided, see bazelbuild/bazel#3935. Instead @rules_python//python:proto.bzl is recommended. I attempted switching to this library, but it's not compatible with @com_google_googleapis's py_proto_library targets, see #69. I found a hacky workaround by using cc_proto_library to generate python targets, but downstream integration into Envoy failed (envoyproxy/envoy#30159).

This PR migrates py_proto_library implementation to to @com_github_grpc_grpc. This implementation is used by @com_google_googleapis's, and, more importantly, uses bazel aspects. Which decouples cncf/xds and Envoy's dependencies from concrete upstream py_proto_library implementations.

This resulted in a significant code improvement of bazel/api_build_system.bzl:

No more custom @com_google_googleapis dependency mapping needed via py_proto_library rules override.
No more hardcoded dependencies _xds_py_proto_library - proto dependency tree is determined from proto_library definitions via Basel aspects.
No more EXTERNAL_PROTO_PY_BAZEL_DEP_MAP dependency map needed - for the same reason.
Similar work in Envoy: envoyproxy/envoy#30834.

Signed-off-by: Sergii Tkachenko <sergiitk@google.com>

Signed-off-by: Sergii Tkachenko <sergiitk@google.com>

Signed-off-by: Sergii Tkachenko <sergiitk@google.com>

Signed-off-by: Sergii Tkachenko <sergiitk@google.com>

Signed-off-by: John Howard <howardjohn@google.com>