Upgrade to github.com/graph-gophers/dataloader/v7

[felixhromadko]

The v7 of the library allows using generics in the key / result. We should consider upgrading to it.

Definition in v5 (current):

	CompetenceLoader  *dataloader.Loader

Definition in v7:

	CompetenceLoader  *dataloader.Loader[string, db.Competence]

This would allow us to remove these functions, especially the somewhat dangerous casting .([]*db.Competence), because the dataloader -> thunk() is already returning the correct type.

func GetCompetenceParents(ctx context.Context, competenceID string, currentUser *middleware.UserContext) ([]*db.Competence, error) {
	loaders := For(ctx)
	thunk := loaders.CompetenceLoader.Load(ctx, dataloader.StringKey(competenceID))
	result, err := thunk()
	if err != nil {
		return nil, err
	}
	return result.([]*db.Competence), nil
}