Allow extra egress rules for the keda operator ciliumnetworkpolicy

[QuentinBisson]

This PR adds support to be able to add extra egress rules to the ciliumnetworkpolicy if for instance, the prometheus used to scale is outside the cluster as the current ciliumnetworkpolicy only allows egress to the cluster pods and the api-server

Checklist

• [x] I have verified that my change is according to the deprecations & breaking changes policy
• [x] Commits are signed with Developer Certificate of Origin (DCO - learn more)
• [x] README is updated with new configuration values (if applicable) learn more
• [x] A PR is opened to update KEDA core (repo) (if applicable, ie. when deployment manifests are modified)

[JorTurFer]

Thanks for the improvement!