Test alert rule with vmalert ui

[Haleygo]

Is your feature request related to a problem? Please describe

vmalert has it's own web ui, I think it will be nice to test alert rules on it.
It will be different from querying alert expr on vmui, cause alert rule has for.
And it will be different from unittest, cause we can use the real data in datasouce instead of artificial one.

Describe the solution you'd like

Test alert rules on vmalert ui, show details like labels and Annotations.

Describe alternatives you've considered

There is a cool tool https://github.com/kadaan/promutil, we can replace datasource host to vm instance.

Additional information

Alerting rule got for, possibly got keep_firing_for requested by #4529, or future feature "exproff" #2857, it will be difficult to debug with other tool.