Support for blue-green upgrade strategy for GKE node pools

[nkarumanchi27]

Describe the bug
GKE clusters now support both surge and blue/green upgrade strategy for nodepool upgrades. This request is to add support for blue/green node pool upgrade strategy into the gke nodepool module, https://github.com/GoogleCloudPlatform/cloud-foundation-fabric/tree/master/modules/gke-nodepool

Google documentation: https://cloud.google.com/kubernetes-engine/docs/how-to/node-pool-upgrade-strategies
google_container_node_pool resource from the provider seem to already support this functionality: hashicorp/terraform-provider-google#12045

[ludoo]

This was implemented in #1905 .

Can you please check support in modules before opening a new issue?