Support generation of pyi files with py_proto_library

[bluec0re]

🚀 feature request

Relevant Rules

New feature for py_proto_library

Description

protoc v3.20 and above supports to generate .pyi files from protos. Whould be great if py_proto_library would/could generate those as well by using the --pyi_out argument to protoc.

Describe the solution you'd like

A new attribute for py_proto_library to enable/disable the generation of .pyi files and a way to reference them for packaging/editor support.

Describe alternatives you've considered

Switching to https://github.com/grpc/grpc (which has added support here: grpc/grpc#32872), but we don't use grpc and would prefer to stick to primary bazel rules.

[github-actions]

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[bluec0re]

friendly ping