[kube-prometheus-stack] allow custom annotations on prometheus rules

[polak785]

Is your feature request related to a problem ?

In the values, customRules only support to override parameters for and severity, but not annotations.

Describe the solution you'd like.

I want to be able to add annotations in order to declare links that will be in the Alertmanager notifications.

Exemple:

  NodeFilesystemSpaceFillingUp:
    severity: "error"
    annotations:
      dashboard: <web_link>

Describe alternatives you've considered.

NONE

Additional context.

No response