Allow configuration of mesh_certificates on google_container_cluster

[somethingnew2-0]

TL;DR

In order to use mTLS service security with Traffic Director "Mesh certificates" must be enabled on the cluster. Add the ability for all cluster modules in this repository to enable this functionality with a variable.

Terraform Resources

The documentation for `google_container_cluster` with the `mesh_certificates` block
https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/container_cluster#enable_certificates

Instructions for `--enable-mesh-certificates` on GKE cluster in the Traffic Director documentation for setting up mTLS certificates
https://cloud.google.com/traffic-director/docs/security-envoy-setup#create-cluster

Detailed design

This could look like exposing an module variable to configure the underlying `google_container_cluster` terraform resource.


mesh_certificates {
  enable_certificates = var.enable_mesh_certificates
}

### Additional information

_No response_

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[somethingnew2-0]

There is an open PR for this issue that will be merged soon