Remove support for Singleton manifests

[Trenly]

Description of the new feature / enhancement

Creating this issue as I haven’t seen one officially made yet. I know it has been discussed, but not seeing anything formally tracking it.

This would be a potentially breaking change.

As tools to create manifests are now to the point that multimanifests are easy to make, the singleton manifest may be phased out.

Proposed technical implementation details

• Have a warning in the community repo for a period, notifying users that singletons will not be supported in the future
• Transition to a pipeline failure in the community repo
• Eventually fully remove support for singletons in future manifest versions

[sredna]

Why?

As someone that edits the manifest by hand for each release and only supports English, the singleton fits my needs nicely.

Once singleton support is removed I will stop pushing updates to Winget, hopefully the community will fill in for me...