Add Support IPAM object to Allow Load Balancer or Port-forward map to floating IP Address

##### ISSUE TYPE

* Feature Idea

##### COMPONENT NAME

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UI,API,Guest Network

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##### CLOUDSTACK VERSION

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N/A
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##### CONFIGURATION

##### OS / ENVIRONMENT

##### SUMMARY

When a Guest Network was created, the port forward and load balancer features only allow to be configure with pre-existing VM in same Guest Network. Sometime user will deploy self managed virtual ip address to support their application such as keepalived, MetalLB..etc. Today, the user will add a secondary NIC to the one of VM instance and then use the assigned NIC ip address to treat the virtual ip setup. Most of the time, it is unavoidable to use this appoarch when LB pool health check limit to L4 port checking.

I'm wondering if ACS can implement IPAM management abstract under guest network to allow user create IP entities which will able to include into port forwarding or Load balancer member.

##### STEPS TO REPRODUCE

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N/A
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##### EXPECTED RESULTS

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##### ACTUAL RESULTS

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N/A
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The issue identifies UI, API, and Guest Network as the affected components, but names no files or tests. Start by tracing the guest-network port-forwarding and load-balancer workflows. Done means users can create IP entities under a guest network and use them in port-forward and load-balancer mappings.

Written by the indexing model from the issue text.