Admission control via validating webhooks

[v-ctiutiu]

Background

Some operations should be denied ahead of time, before creating the static route CRD.

A few scenarios when this feature comes in handy:

• Creating CRDs with routes that overlap (see Cross CRDs checks for static routes overlapping #13).
• Trying to use protected IPs/subnets in CRDs (see ConfigMap for protected IPs/subnets #11).

Proposal

Check Kopf documentation about Admission Control.