Add order index to versions (similar to gallery images)

Is your feature request related to a problem? Please describe.

Since the versions are always listed in published order, doing things like backporting to older versions of Minecraft make for an odd list where versions seem out-of-order.

Describe the solution you'd like

If versions used a system similar to gallery images, creators could assign sort indexes to manually order their versions.

Specific behaviors:

The "list versions" endpoint would sort by index first, then by published date second. Therefore all existing projects maintain the exact same behavior as they do now.
When creating a new version, default it to the highest index among existing versions, which would always put it at the top if the creator changes nothing (again, preserving current behavior).

Describe alternatives you've considered

Semver-based default sorting, as suggested in modrinth/knossos#307, which presents its own difficulties, especially considering not everyone uses semver.

Additional context

Edit: A neat side effect of this implementation is that creators could even use the sort index as groupings. For example instead of just doing 0, 1, 2, ...etc a creator could give all their versions for 1.18 the index of 118 (or 1180 to account for minor versions) and for 1.19 the index of 119 (1190). That would make all their mods sort into the groups first, then simply order by publish date.

modrinth / code