Adapt KLT mutating webhook to support ReadinessGates

[thisthat]

Goal

Change the mutating webhook to remove the addition of the KLT scheduler if the FF klt.readiness-gate is true

Details

If the FF klt.readiness-gate is true, KLT relies on readiness gate APIs to block deployments to proceed. Hence, we don't need to mutate manifests by adding our scheduler plugin.

DoD

• If klt.readiness-gate is false, the webhook behaves like the past
• If klt.readiness-gate is true, the webhook doesn't add the scheduler
• Kuttl tests

Dependency

• Support controller runtime v0.15.0 #1457

[odubajDT]

This functionality is already in place, closing this ticket