Add support for generating per-namespace EgressGatewayPolicies

[simu]

The feature generates policies that expect the configured egress range to be implemented according to the design selected in https://kb.vshn.ch/oc4/explanations/decisions/cloudscale-cilium-egressip.html

Checklist

• The PR has a meaningful title. It will be used to auto-generate the
  changelog.
  The PR has a meaningful description that sums up the change. It will be
  linked in the changelog.
• PR contains a single logical change (to build a better changelog).
• Update the documentation.
• Categorize the PR by adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog.

[bastjan]

Good work on the debug labels/ error handing!