Add apps support

[davidanthoff]

More a proof of concept at the moment.

Definition of an app looks like https://github.com/davidanthoff/examplejlapp.

To add an app:

juliaup app add https://raw.githubusercontent.com/davidanthoff/examplejlapp/main/

To run the app:

juliaup app run jlappexe1 arg1 arg2
juliaup app run jlappexe2 arg1 arg2

To remove the app:

juliaup app remove ExampleJlTestApp

Lots and lots of things that would need to be added:

• Handling of even the most basic errors :)
• Shims
• Registry story
• Updates
• Status
• Maybe the app commands should actually have their own app, like jlapp add ...
• Handle installs of apps into different depots

[davidanthoff]

Some relevant links for the next steps:

• https://learn.microsoft.com/en-us/windows/uwp/launch-resume/hosted-apps#declare-a-hosted-app
• https://learn.microsoft.com/en-us/windows/apps/desktop/modernize/grant-identity-to-nonpackaged-apps

[simeonschaub]

Are you aware of JuliaLang/Pkg.jl#3772? I think this would be good to coordinate with that PR so we don't have two completely separate notions of apps in the Julia ecosystem