Enhancement: Support templating and time

[huanggze]

The Dashboard CRD defines three major fields: panels, time and templating.

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)

time provides ways to configure the time ranges of the data being displayed. (See Grafana's Time range controls)

[benjaminhuo]

Contributors are welcomed for these improvements KubeSphere custom dashboard template samples and their corresponding grafana dashboard linkscan be found in https://github.com/kubesphere/monitoring-dashboard/tree/master/contrib/gallery

[zhu733756]

backend has fixed by #9 , frontend should support for templatings.