Feature Request: annotating rule for spec.matches.labelSelector

[dulltz]

I would like to use Constraint's spec.match.labelSelector,
but konstraint seems to only supports spec.match.kinds now. (ref)

Also, as described in #56, rerunning of konstraint create erases existing spec.match.labelSelector.

We should support an annotation rule for generating spec.matches.labelSelector.

[dulltz]

I want to add annotation rules like the following example.

Supporting all representations of labelSelector with annotation rules would be complicated, so I think it is simpler to support only matchLabels.

# @matchlabels app=a team=b
package foo

import data.lib.core
...

↓

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: Foo
metadata:
  name: foo
spec:
  match:
    labelSelector:
      matchLabels:
        app: a
        team: b

[jalseth]

I think this approach makes sense. We will start with matchLabels and we can look into adding support for matchExpressions if that is requested in the future. If you have the time, we'd welcome a PR to add this!

[dulltz]

@jalseth
I created the PR #94. May I ask for your review?

[jalseth]

Implemented in #94