3scale monitoring deploys prometheus rules as opt-in feature

Currently, when enabling the monitoring of 3scale, two monioring assets are created: grafana dashboards and prometheus rules.

Release engineers have reported their concern about the prometheus rules being very infraestructure specific.

The 3scale operator currently reconciles the prometheus rules, reverting any change made manually to them. The main reason to do so is to provide upgrading features. If manual update would be allowd, then upgrading would remove those manual updates and this would be totally unexpected by the customer.

The idea is to add an option to disable the deployment of prometheus rules.

apiVersion: apps.3scale.net/v1alpha1
kind: APIManager
metadata:
  name: apimanager1
spec:
  wildcardDomain: example.com
  monitoring:
    enabled: true
    enablePrometheusRules: false <- by default would be true

The 3scale operator team would also publish in GH (or any other public repo) prometheus rules as templates to be used by customers to use them with their own customizations.

Another option would be to totally remove the prometheus rules when deploying monitoring resources. Always leave up to the customer the deployment and lyfecycle management of the prometheus rules. We would always provide public examples and templates for easy setup.