1. Proposed title of this feature request

allow ROSA to enable setting V4InternalSubnet during install process to avoid network CIDR conflict 

2. What is the nature and description of the request?

The default CNI is OVNKubernetes for 4.11 and above, this is mandatory and not able to change back to OpenshiftSDN for now 

https://docs.openshift.com/rosa/networking/cidr-range-definitions.html

If CX has an existing VPC containing 100.64.0.0/16 range, it might causing IP address conflicts can arise leading to unpredictable behavior.

 
It is possible to configure the IP range in On-Perm OCP 4.12 and later versions via the V4InternalSubnet by dropping manifests during the installation process.

However, this feature is not compatible with ROSA, OSD, and ARO yet for now.
3. Why does the customer need this? (List the business requirements here)

CX like to keep using and installing new ROSA cluster with OVN  in their existing 100.64.0.0/11 VPC

4.10 with openshiftSDN is going to EOL soon.

4. List any affected packages or components.

OVN-Kubernetes