Update UnattendedInstallFiles.cs (AWS-2024-006)

[GhostlyBox]

Including checks for .vmimport files as per following references:

https://aws.amazon.com/security/security-bulletins/AWS-2024-006/ https://www.immersivelabs.com/blog/the-return-of-unattend-xml-revenge-of-the-cleartext-credentials/