feat(controller): add support for mute timing

[chenlujjj]

To resolve: #1723

[chenlujjj]

tested in local:

---
apiVersion: grafana.integreatly.org/v1beta1
kind: GrafanaMuteTiming
metadata:
  name: mutetiming-sample
spec:
  instanceSelector:
    matchLabels:
      dashboards: "grafana"
  name: mutetiming-sample
  editable: false
  time_intervals:
    - times:
        - start_time: "00:00"
          end_time: "06:00"
      weekdays: ["saturday", "sunday"]
      days_of_month: ["1", "10"]
      location: "Asia/Shanghai"

result:

[theSuess]

Thanks for the PR! I'll take a look at this soon. It's too big of a change for the next release, but we'll get it out soon now that the holiday season is over