Generate scaffold for Cloud Storage

[coryan]

We can generate all the admin (and unary) operations for the .google.storage.v2.Storage service. It will not be functional at first, but can give us a sense of what is missing.

To get a full client we need to:

• Generate code for methods without HTTP annotations
• Generate the scaffold with code skipped to get started
• Implement routing annotation #1819
• Temporarily suppress documentation for client builders
• Temporarily suppress documentation links in request builders
• Generate correct documentation links for request builders
• Write a basic client selectively exposing RPCs
• Rename the crate to google-cloud-storage-control
• Figure out a story for test coverage of veneers
• Figure out a story for mocking veneers
• Refactor the code to convert google.rpc.Status (maybe) handling some custom details.