Enhancement: Support templating and time

The Dashboard CRD defines three major fields: [panels](https://github.com/kubesphere/monitoring-dashboard/blob/master/api/v1alpha1/dashboard_types.go#L35), [time](https://github.com/kubesphere/monitoring-dashboard/blob/master/api/v1alpha1/dashboard_types.go#L33) and [templating](https://github.com/kubesphere/monitoring-dashboard/blob/master/api/v1alpha1/dashboard_types.go#L37).

In KubeSphere 3.0.0, the front end has implemented the field `panels`. In future releases, we can improve on `templating` and `time`.

`templating` describes user-defined placeholders for a value which can be used in PromQL expression writing. Like Grafana, we should support both dynamic variables, constants and much more. (See [Grafana's Templates and Variables](https://grafana.com/docs/grafana/latest/variables/))

`time` provides ways to configure the time ranges of the data being displayed. (See [Grafana's Time range controls](https://grafana.com/docs/grafana/latest/dashboards/time-range-controls/))