Update auto-deployed prometheus scrape config

What does this MR do?

Updates the prometheus.yml settings for the Prometheus server deployed on the clusters page. It addresses two needed items:

1. Scrape of cAdvisor metrics for k8s 1.7+
2. Metric relabeling rules to properly detect the environment for k8s cpu/memory metrics

Screenshots if relevant:

Prometheus was successfully installed on your cluster message:

Pod running on the cluster:

ConfigMap created successfully with the proper values:

How to test:

1 - Install Cloud SDK

2 - Install and setup kubectl

3 - Create a Cluster and install Prometheus through the application section. This takes around 5 minutes

4 - Run the following command on your terminal:

gcloud container clusters get-credentials <name-of-cluster> --zone us-central1-a --project gitlab-internal-153318

5 - Run kubectl proxy on your terminal

4 - Go to the UI: http://127.0.0.1:8001/ui

6 - Check values-content-configuration on the ConfigMap are correct

What are the relevant issue numbers?

Closes #41796 (closed)