FIX: Propagate Slack channel Override

[jescarri]

This PR fixes a bug that prevents routing slack messages to the configured target channels.

Related to: #458

Testing done:

Config file:

slack:
  channels:
    - channel: kyverno-reports1
      customFields:
        cluster: TestCluster
      filter:
        namespaces:
          include:
          - team1-a
          - team1-b
        policies:
          include:
          - test-policy
        priorities:
          include: warning
      name: team1
      skipExistingOnStartup: false
      sources:
      - kyverno
      webhook: https://slack.webhook
    - channel: kyverno-reports2
      customFields:
        cluster: TestCluster
      filter:
        namespaces:
          include:
            - team2-a
        policies:
          include:
          - test-policy
        priorities:
          include: warning
      name: team2
      skipExistingOnStartup: false
      sources:
      - kyverno
      webhook: https://same-slack-webhook-as-team1

Output

{"L":"INFO","T":"2024-07-09 16:12:34","C":"config/resolver.go:87","M":"API BasicAuth enabled"}
{"L":"INFO","T":"2024-07-09 16:12:34","C":"config/target_factory.go:351","M":"team1 configured"}
{"L":"INFO","T":"2024-07-09 16:12:34","C":"config/target_factory.go:351","M":"team2 configured"}
{"L":"INFO","T":"2024-07-09 16:12:34","C":"cmd/run.go:152","M":"start client","worker":5}
{"L":"INFO","T":"2024-07-09 16:12:35","C":"kubernetes/policy_report_client.go:63","M":"informer sync completed"}
{"L":"INFO","T":"2024-07-09 16:12:35","C":"http/utils.go:51","M":"team1: PUSH OK"}
{"L":"INFO","T":"2024-07-09 16:12:35","C":"http/utils.go:51","M":"team2: PUSH OK"}
{"L":"INFO","T":"2024-07-09 16:12:35","C":"http/utils.go:51","M":"team2: PUSH OK"}

Slack messages are routed properly

[fjogeleit]

thanks, will try to release a fixed version end of the week

[jescarri]

you are welcome thanks for the quick merge.