Add schema for Cinnamon Spice metadata info.json

[JEleniel]

Schema for the info.json metadata file of a Cinnamon Spice, as documented at: https://github.com/linuxmint/cinnamon-spices-extensions, https://github.com/linuxmint/cinnamon-spices-applet, https://github.com/linuxmint/cinnamon-spices-desklets, and https://github.com/linuxmint/cinnamon-spices-themes

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @madskristensen and @hyperupcall - if they write a comment saying "LGTM" then it will be merged.

[hyperupcall]

Thanks! Could you remove pnpm-lock.yaml?- (we use the npm lockfile).

One more thing, info.json is too generic a name, so I won't be able to merge this since it would potentially create too many false positives. You can see the this CONTRIBUTING.md section on alternative names (or removal of fileMatch)