Handle wavefrontalert deletion when it associated with alertsconfig

[lilwan]

Is this a BUG REPORT or FEATURE REQUEST?:
feature

What happened:
We can have a wavefrontalert with exported params and associated with multiple alertsconfig, and then if we delete this wavefrontalert, the current code deletes the individual alert in wavefront but does not update the alertsconfig

What you expected to happen:
When the wavefrontalert template got deleted, we should update alertsconfig as well

How to reproduce it (as minimally and precisely as possible):

1. Create a wavefrontalert template with exported params and associated with a alertsconfig.
2. Delete this wavefrontalert
3. wavefront alert is deleted from wavefront
4. alertsconfig still has it in the status

Anything else we need to know?:

Environment:

• alert-manager version
• Kubernetes version :

$ kubectl version -o yaml

Other debugging information (if applicable):

- controller logs:

$ kubectl logs