Add option to create sources.msix file for private repo

[pquiring]

Description of the new feature / enhancement

Would be nice to create my own repo with a simple command.
Plan to host repo on sourceforge.net (only supports PHP) so I think the REST option is not possible.
Need a new command to create sources.msix for use in private repo.

Proposed technical implementation details

wingetcreate cache --build --output=folder/path/sources.msix
wingetcreate cache --sign --output=folder/path/sources.msix

[pquiring]

I've tried to add "one" package to winget-pkgs and it's taking days. Once I release and update dozes of packages that would be unacceptable slow :(