GKE deployment manager, add support for isito 0.7

[mukundha]

Is this a BUG or FEATURE REQUEST?:
Request

Did you review https://istio.io/help/ and existing issues to identify if this is already solved or being worked on?:
Yes

Feature Request:
Y

Describe the feature:
GKE Deployment manager support only versions 0.5 and 0.6, can we pls add support for 0.7

https://pantheon.corp.google.com/launcher/config?templateurl=https:%2F%2Fraw.githubusercontent.com%2Fistio%2Fistio%2Fmaster%2Finstall%2Fgcp%2Fdeployment_manager%2Fistio-cluster.jinja&pli=1

Thanks,