ParseErrors for unknown enum responses for GAPICs over REST

[busunkim96]

When a REST endpoint adds a new enum to a response, older versions of the GAPIC library without the enum definition raise parse errors.

Details and status in this document.

See https://github.com/googleapis/python-compute/issues/111

[vchudnov-g]

We are working on server-side support for solving this. See internal docs.

[parthea]

Converting to feature request