Add Modrinth Support

[glowredman]

(From the pack design doc)

Most work has already been done in order to create an MMC archive. The Modrinth archive specifications can be found here. Publishing a new release can be automated by interacting with the Modrinth API:

• Creating a new version: https://docs.modrinth.com/api-spec/#operation/createVersion
• Example for POSTing a new archive: https://github.com/wafflecoffee/website/blob/main/packwiz/mrupload.sh#L23-L26

One thing left to do is change all download URLs in gtnh-modpack.json to use any of the whitelisted URLs (cdn.modrinth.com, github.com, raw.githubusercontent.com, gitlab.com) or ship them as part of the archive:

(Source)