Validation for pod and node cidr ranges if the same router id is used

[DockToFuture]

How to categorize this issue?

/area networking
/kind enhancement
/platform openstack

What would you like to be added:
A validation for shoot clusters with not managed by gardener networks and routers. The validation should check before cluster creation if the pod cidr range and node cidr ranges is overlapping with another shoot cluster within the project where the network and router ids are the same as in the cluster to create (not managed by gardener cluster).
When the pod cidr range or node cidr range in thus a case is overlapping, cluster creation should be forbidden/denied with a corresponding output message.

Why is this needed:
To prevent issues where the cloud controller managers running in the controlplane of the affected clusters are competing for routes within the same network and router. This could lead to disfunctional clusters and in the worst case bring down neutron.