Deprecate Prepare DHCP IP addresses pool documentation

**What happened**:

As vSphere Cluster admin, I should have existing DHCP configuration setup. EKSA documentation have `Prepare DHCP IP addresses pool` documentation section which is confusing to create new DHCP setup and IP pool instead, existing DHCP and ip configuration can be used.

**What you expected to happen**:

I am raising this issue to review and remove any outdated documentation for DHCP setup doc section.

https://anywhere.eks.amazonaws.com/docs/clustermgmt/cluster-upgrades/vsphere-and-cloudstack-upgrades/#prepare-dhcp-ip-addresses-pool

**How to reproduce it (as minimally and precisely as possible)**:
- documentation changes
**Anything else we need to know?**:

**Environment**:
- EKS Anywhere Release: new cluster setup, onboarding
- EKS Distro Release: new cluster setup, onboarding

Start with the linked “Prepare DHCP IP addresses pool” section in the EKS Anywhere vSphere and CloudStack upgrades documentation. Review whether the section is outdated or confusing for administrators with existing DHCP, then remove or revise that documentation so it no longer implies a new DHCP setup is required.

Written by the indexing model from the issue text.