To close this PR we should demonstrate that librarian generate produces a library for google/cloud/security/publicca/v1. In addition to the functionality from "[1] Swift: ...." the library should now be able to send an HTTP request for the one service (and one RPC) in this API. The RPC should:

• Allow callers to set the request parameters.
• If successful, parse the HTTP response and return that to the caller.
• If failed, raise some (unspecified) error type.

Out of scope: parsing the error types
Out of scope: implementing a retry loop
Out of scope: implementing pagination (the service does not have them).
Out of scope: implementing LROs (the service does not have them).