[aws][installer] Collab: AWS: Cross-Account Shared VPC Installs

• As a user I would like to install a cluster in existing VPC with Shared Subnets, providing my own Private Hosted Zone, so I can follow best practice on AWS in my deployment.

Goal:

• Investigate limitations when deploying a cluster in existing VPC with shared subnets using also shared PHZ. Part of that feature was covered on CORS-1666
• SPLAT team is working in collab Installer team to troubleshoot issues using this feature. The goal here is to understand the PoC and limitations, providing examples and document the flow used to resolve the final problem (in production) in Collab with Installer team, and eventually Network Edge team.

Engineering references:

• https://redhat-internal.slack.com/archives/C68TNFWA2/p1681837202378159