Add "cause based" alerts for DNS operator

[R-Lawton]

WHAT

Create cause-based alerts for the dns-operator

The tabletop scenarios can be used as inspiration for the alerts

possible alerts:

• cannot access DNS Provider
• conflicted default GEO

DONE

• Create alerts for different scenarios for DNS operator
• Create Promtool unit tests for each new alert

[philbrookes]

@R-Lawton can we get some information on how to setup and develop against alert manager locally?

[maleck13]

going to move this beyond v1 as we will add a dashboard and the status will report if we cannot access a DNS provider, we will also add a doc to cover common causes of conflict #776