Adding support for Installing Scripts from a repository.

[TechDufus]

This PR adds support for installing scripts from a repository.

This operates almost exactly the same way that the DependencyType PSGalleryModle does.

This adds a new PSDependMap that calls the PSDepend\PSGalleryScript.ps1 file.

An example requirements.psd1 file would look like this

@{
    PSDependOptions = @{
        Target     = 'CurrentUser'
        DependencyType = 'PSGalleryScript'
    }

    'pwshfetch-test-1' = 'latest'
}

Which would be the same as running

Install-Script pwshfetch-test-1 -Scope CurrentUser