SCM Generator Enhancement: Exclusion Labels

[DaytonG]

Summary

I'm using the SCM generator to gather a list of repositories from a private gitlab enterprise server. I would like to use a label to exclude repos, like block-deploy to instead deny certain repos from being deployed.

Motivation

We split our gitlab groups into separate areas per company effort. Some of those projects are in the incubation phase, and should be ignored in certain environments. It would be nice to assume that all "deploy-.*" repos are available and instead exclude repos using repo tag metadata. Less repos to touch.

Proposal

The first idea that comes to mind is to add a new "excludeLabel" filter type.

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: myapps
spec:
  generators:
  - scmProvider:
      filters:
      - repositoryMatch: ^myapp
        pathsExist: [kubernetes/kustomization.yaml]
        # a new filter that checks for the presence of a label. If found: ignore the repo
        excludeLabel: "block-deploy"
  template:
  # ...

That being said, I'm not familiar with the code structure of filters.

[crenshaw-dev]

I think we should use matchExpressions, similar to the request for PR generators: #12300