Add missing command to apply updates to GKE cluster

[diavrank]

File: themes/default/content/registry/packages/gcp/installation-configuration.md

Hi, I was able to run the example app of kubernetes-ts-multicloud for GKE cluster, however, I noticed that when we update the pulumi code, it threw authentication errors like:

kubernetes:apps/v1:Deployment (gke-demo-app):
    error: configured Kubernetes cluster is unreachable: unable to load schema information from the API server: Get "https://<ip_address>/openapi/v2?timeout=32s": getting credentials: exec: executable gke-gcloud-auth-plugin not found
    
    It looks like you are trying to use a client-go credential plugin that is not installed.
    
    To learn more about this feature, consult the documentation available at:
          https://kubernetes.io/docs/reference/access-authn-authz/authentication/#client-go-credential-plugins
    
    Install gke-gcloud-auth-plugin for use with kubectl by following https://cloud.google.com/blog/products/containers-kubernetes/kubectl-auth-changes-in-gke

So, after installing the plugin with the below command, I was able to apply the updates.

gcloud components install gke-gcloud-auth-plugin

Which updates did I do?

I had a local cluster with minikube and I left the local cluster configuration uncommented so I got some errors regarding the static IP address for such cluster, so, that provoked to fail the process of my GKE cluster. To fix it, I had to comment out the local cluster configuration but then I got the above error about the GKE command plugin, and after installing it, I was able to create the missing resources for my GKE cluster and now everything is working as expected.

So, I recommend updating the documentation by adding that command as a prerequisite to authenticating to GCP with Pulumi.

Thanks!

[desteves]

https://www.pulumi.com/registry/packages/kubernetes/how-to-guides/kubernetes-ts-multicloud/

Add pre-req for golang.
Update the README