Reserve IP address for out of bounds machines

Ability to define IP address beside of choosing VMs in Static NAT, Port Forward and Load balancer services to provide those services to servers outside of CloudStack.
##### ISSUE TYPE

* Feature Idea

##### COMPONENT NAME

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VR
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##### CLOUDSTACK VERSION

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All versions
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##### CONFIGURATION

Advanced networking

##### OS / ENVIRONMENT

N/A

##### SUMMARY

In some network services we need to specify which VM should use it. For example Static NAT, Port Forward and Load balancer.
It would be a good idea if we can also specify IP address of a server which is not managed by CloudStack.
This feature helps us to use network services provided by virtual router for physical servers or even VMs outside of CloudStack management area but share a common L2 network with other VMs in CloudStack.
This feature also requires reserve IP address capability in all type of networks. We can expand the issue #4357 for private IPs in isolated networks too.

##### STEPS TO REPRODUCE

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1. Create an isolated network
2. In Port forward section define a new rule
3. In "Add VM" panel write IP address of the server outside of CloudStack

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##### EXPECTED RESULTS

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An iptables rule created in virtual router to forward desired port to the server IP

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##### ACTUAL RESULTS

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It is not possible to mention IP address of the server outside of CloudStack

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Iniziare con le implementazioni del router virtuale di CloudStack per Static NAT, il port forwarding e il bilanciamento del carico, quindi esaminare l’issue #4357 per il lavoro correlato alla prenotazione di IP private. Il lavoro è completato quando questi servizi possono utilizzare come destinazione un IP esterno alla gestione di CloudStack e il router virtuale crea la regola di inoltro corrispondente per tutti i tipi di rete supportati.

Scritto dal modello di indicizzazione a partire dal testo della issue.