fix: Generate gRPC files for long-running operations

[boimart1]

Fixes #12 🦕

(My automatic whitespace formatter removed some trailing whitespace, is this an issue?)

Note that I'm not entirely sure how to work with synthtool, and so I couldn't figure out how to get the license header and formatting fixed before committing the files generated by nox -s generate_protos. Someone else is going to have to do that part for me 🙂 Still, the generated grpc file looks good.

[boimart1]

Ah, actually, it looks like there are some more import weirdnesses than I expected. The committed
operations_pb2 expects operations_grpc_pb2 to have from operations_proto_pb2 import *, which is what allows it to have access both to the messages and the service definitions... I'm not entirely sure what to do with this 🤔

[boimart1]

I'm thinking of leaving the grpc file to its generated name operations_pb2_grpc.py, and having another "redirect" file (like the current operations_pb2.py) which would amount to:

# operations_grpc_pb2.py
from google.longrunning.operations_proto_pb2 import *
from google.longrunning.operations_pb2_grpc import *

This would ensure that all users who currently import either operations_pb2 or operations_grpc_pb2 continue to work as expected.

The only mild downside is the naming mess.

[busunkim96]

I think the naming mess is kind of unavoidable at this point. 🤷 I'll ping some folks to see if they have more historical context on the LRO directory.

Thank you for the PR!