Enable `secondary_iso_images` to Retrieve and Checksum ISO Images just like `iso_url`

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#### Description

I like that `iso_url` uses Go-Getter to fetch and optionally checksum an ISO, but find it strange that `secondary_iso_images` does not have the same features. Rather, it seems like this just gets piped directly into Hyper-V as other ISOs to mount.

#### Use Case(s)

1. Installing additional software from the internet or a network share.
2. Wanting to ensure that software being installed has the same checksum as when you wrote the template, especially since the software is likely being installed from an elevated session in Windows or root session in Linux, where it would be vulnerable to a supply chain attack.

#### Potential configuration

Either parse the `secondary_iso_images` variable through the same code that handles `iso_url` _or_ provide a new option called `secondary_iso_image_urls` that are processed through Go-Getter and can get appended to the ISO URLs passed into Hyper-V if they are provided.

#### Potential References