Add support for resourcePolicy property to ResourceRecordSet

[davemcphee]

Is your feature request related to a problem? Please describe.
cloud-dns API supports various new resource policies, but this library only supports "Default" type. Any resourcePolicy data from the API is quietly dropped.
Describe the solution you'd like
I'd like to be able to use this library to manage GeoIP and Weighted routing policies, as well as the currently supported "Default" type.
Additional context
This issue is being opened to track an incoming PR that adds this feature.

[vchudnov-g]

Thanks for reporting this issue and suggesting a fix! We'll work on this.