Add Networking metadata to Libvirt XML

### The required feature described as a wish

Libvirt allows for adding Metadata to the XML of a Domain: https://libvirt.org/formatdomain.html#general-metadata

We can use this Metadata to add additional information of the Instance so that it can be used by Libvirt hooks: https://libvirt.org/hooks.html#etc-libvirt-hooks-qemu

My proposal is to add basic IP address information to the XML:

```

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Hooks can prepare additional firewalling or routing on the host while it is booted, this is up to the admin to decide.

首先追蹤 CloudStack 如何產生 Libvirt 網域 XML，並檢閱 issue 中連結的 Libvirt 網域中繼資料與 hook 文件。當產生的 XML 為適用的 IPv4 與 IPv6 網路包含所要求的網路位址中繼資料，包括位址、前綴、系列、橋接與 VLAN 值時，工作即完成。

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