feat: recurring silence

[zasdaym]

Resolves #363.

Checklist

• Update changelog in CHANGELOG.md.

[QuentinBisson]

Hey @zasdaym thank you for your contribution, I will try to take a look at the approach before the end of the month

[QuentinBisson]

I think it would make sense to do it the same way it is done with kubernetes jobs. Can you compare the 2 ways? Same for timezones

[QuentinBisson]

I am not sure this works because silences were not thought of as templates. Where are you specifying the start and end date of the silence?

[QuentinBisson]

Okay I see what you did with createSilence but the end is still missing right? Can you check the cr example I posted at the end?

[QuentinBisson]

Also i think this PR makes sense (instead of the current annotation way) #580 and this would invalidate this. I would probably rebase your branch on the one I linked

[QuentinBisson]

This should probably be a v1alpha1 but use the silence v1alpha2 spec

[zasdaym]

Why? v1alpha1 is already deprecated right?

[QuentinBisson]

@zasdaym what do you think about this CRD instead?

apiVersion: observability.giantswarm.io/v1alpha1
kind: RecurringSilence
metadata:
  name: nightly-silence
  namespace: foo
spec:
  schedule: "0 0 * * *"
  duration: "2h"
  matchers:
    - name: severity
      value: warning
      matchType: "="

[zasdaym]

@zasdaym what do you think about this CRD instead?

apiVersion: observability.giantswarm.io/v1alpha1
kind: RecurringSilence
metadata:
  name: nightly-silence
  namespace: foo
spec:
  schedule: "0 0 * * *"
  duration: "2h"
  matchers:
    - name: severity
      value: warning
      matchType: "="

Seems OK, I've updated my PR to use this spec.