Add support for building windows images for Nutanix

[mpanduru]

Add support for building Windows images for Nutanix by introducing image_type=Nutanix.
Nutanix provides its own VirtIO drivers ISO, which differs from the Fedora VirtIO ISO both in contents and in folder structure (including legacy Windows folder naming in newer releases).
When image_type=Nutanix is used, the build process now expects the Nutanix VirtIO drivers ISO and uses Nutanix-specific folder mappings to locate and inject the appropriate drivers.

Fedora VirtIO ISO layout:

<driver>/<windows-version>/<arch>/
.
└── viostor/
    └── 2k22/
        └── amd64/
            └── *.inf, *.sys, *.cat

Nutanix VirtIO ISO layout:

<Windows version folder>/<arch>/ (some versions include "(Legacy)" in the folder name)
e.g.
.
└── Windows Server 2019/
    └── x64/
        └── *.inf, *.sys, *.cat
└── Windows 7 (Legacy)/
    └── x64/
        └── *.inf, *.sys, *.cat