Mono-manifest

[theRealPadster]

Work-in-progress PR for discussion and so that I can sync main down

TODO:

• Get user/repo/branch working (it only passes in the manifest data when using mono-manifest)
• Need a repo for custom apps (or add a key to denote app vs extension, and extra logic)
• Write node.js script to scan items in monomanifest and fetch star counts from github, then update the monomanifest
• Write a workflow to automate/schedule this
• Add optionality to extensions (@CharlieS1103 )
• Add optionality to custom apps (@CharlieS1103 )

[rxri]

Closing due to different marketplace behavior in v3 and I'm unsure that this pull request would be merged before v3 release.