Add NGINX exporter for Kubernetes deployments

We currently do not have any metrics for NGINX which is something we have currently on VMs.

https://github.com/nginxinc/nginx-prometheus-exporter/blob/master/README.md

It does look like this is supported in the Chart https://docs.gitlab.com/ee/user/project/integrations/prometheus_library/nginx_ingress.html#about-managed-nginx-ingress-deployments so maybe it's just a matter of enabling it.

Milestones:

• Confirm nginx exporter is enabled
• Enable scraping of the nginx exporter