This PR onboards the google-cloud-workflows package to librarian. Note that this package contains overlapping api-paths which requires the following:

• Allow the cli tool to copy code into owl-bot-staging even if the directory exists.
• Ensure that the order of the api paths is not changed i.e. the google/cloud/workflows/executions api paths are followed by google/cloud/workflows/ api paths in state.yaml file.

For the latter point, this solution is consistent to how the config is specified in .Owlbot.yaml to allow the post processor to override and use the correct package name in files such as setup.py.

We may not need to care about the order of the api paths if the module name is specified as google.cloud.workflows for the executions api in its BUILD.bazel file. Alternatively, this can be passed down as a generator option to protoc in .generator/cli.py. This means that we'll need to hardcode such api paths within this file and add conditional logic which adds a little more complexity. This solution is more robust but can be done as a follow up if needed.

Towards googleapis/librarian#762 🦕