Add support for other sources of Scoop app and main bucket

[Karsten A. M. Guenther]

Description:

I love Scoop and want to support "offline" usage in my company. Therefore I tackled an already existing TODO:

Install/install.ps1

Line 680 in 656e17b

 # TODO: Use a specific version of Scoop and the main bucket 

[Karsten A. M. Guenther]

Any review and improvement comments are welcome.

[Karsten A. M. Guenther]

@rashil2000 @chawyehsu Hi, any feedback on this change from your side would be very welcome.