feat: contact point overrides

[theSuess]

Allows users to override settings using config maps or secrets.

I've intentionally not used the templating logic of data sources as IMHO this will cause more issues downstream, especially with contact point templates.

An example contact point would look like this:

apiVersion: grafana.integreatly.org/v1beta1
kind: GrafanaContactPoint
metadata:
  name: grafanacontactpoint-sample
spec:
  name: grafanacontactpoint-sample
  type: "email"
  instanceSelector:
    matchLabels:
      instance: my-grafana-cloud-stack
  settings:
    addresses: [email protected]
  valuesFrom:
    - targetPath: subject
      valueFrom:
        secretKeyRef:
          name: super-secret-data
          key: secret-subject

which will result in:

apiVersion: 1
contactPoints:
    - orgId: 1
      name: grafanacontactpoint-sample
      receivers:
        - uid: 5628b3a0-8fb1-44a8-a694-46bb8849c484
          type: email
          settings:
            addresses: [email protected]
            subject: <value-from-secret>
          disableResolveMessage: false

Fixes: #1595