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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从 CloudStack 针对 Static NAT、端口转发和负载均衡的虚拟路由器实现开始，并查看 issue #4357 了解相关的私有 IP 预留工作。当这些服务可以将 CloudStack 管理范围之外的 IP 作为目标，并且虚拟路由器能够在所有受支持的网络类型中创建相应的转发规则时，即视为完成。

由索引模型根据 Issue 内容生成。