refactor(contributors): move order to pivot table

[czaja307]

No description provided.

[github-actions]

Looks like you did not link an issue to this PR. If this PR completes a task, consider linking it.

[mini-bomba]

there's a reason why we didn't add the order field to the pivot table
the reason being that the API would absolutely suck to use (changing the value would involve deleting and recreating the relationship)

i see two solutions:

• either make the pivot table an actual table & model (breaking change)
• or hack in a way to modify n:m relationship properties (which honestly shouldn't be that difficult, it would just be jank, as we'd be circumventing adonis' model system)