add monitor and rules resources to user-facing roles

[jouve]

Description

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request. If it fixes a bug or resolves a feature request, be sure to link to that issue.

in cluster with separation between (cluster) admin and (namespaced) users, it allows the namespaced users to create monitor and rules in their namespaces according to the default k8s model of user-facing roles.

defined as an addon to have the feature disabled by default and simple to enable.

ref: https://kubernetes.io/docs/reference/access-authn-authz/rbac/#user-facing-roles

Type of change

What type of changes does your code introduce to the kube-prometheus? Put an x in the box that apply.

• [ ] CHANGE (fix or feature that would cause existing functionality to not work as expected)
• [x] FEATURE (non-breaking change which adds functionality)
• [ ] BUGFIX (non-breaking change which fixes an issue)
• [ ] ENHANCEMENT (non-breaking change which improves existing functionality)
• [ ] NONE (if none of the other choices apply. Example, tooling, build system, CI, docs, etc.)

Changelog entry

Please put a one-line changelog entry below. Later this will be copied to the changelog file.

- add monitor and rules resources to user-facing roles (addon)