Add example steps for deploying WordPress on GKE

[devdattakulkarni]

Currently, the WordPress example steps are defined for Minikube.

We should add steps for deploying WordPress on GKE.

The main change with GKE is that when we create the provider kubeconfig, we need to provide it the IP address of the API server as command-line flag. Currently, this is not documented anywhere. As part of a related issue, we should update the documentation in README and also the help text output by provider-kubeconfig.py to indicate when to use the "-s" flag.

[devdattakulkarni]

Specifically, we should modify step 3 to the following:

`
3. Get Provider and consumer kubeconfigs:

• Extract provider kubeconfig:
  $ KUBEPLUS_NS=default
  $ python ../../../provider-kubeconfig.py create $KUBEPLUS_NS
• If your cluster is on public cloud (such as GKE/EKS/AKS), then follow these steps:
  $ wget https://github.com/cloud-ark/kubeplus/blob/master/parse-api-server-url.sh
  $ ./parse-api-server-url.sh
  $ python ../../../provider-kubeconfig.py -s 'output-from-above-command' create $KUBEPLUS_NS
  `