Fix creators re-ordering bug

[NicolasPennie]

Overview

A DB conflict would happen when the same creator would change positions in the creators array. This caused the update to drop and the NFT indexing to fail:

Original state:

(A, 1)
(B, 2)
(C, 3)
(D, 4)
(E, 5)

New data:

(A, 1)
(C, 2)  // This conflicts with (C, 3)
(D, 3)  // This conflicts with (D, 4)
(E, 4)  // This conflicts with (E, 5)

The fix is to remove the unique constraint. We do not need it. The explanation is included in the code, under the migration changes. I'll copy them here for clarity:

We no longer want to enforce uniques on the (asset_id, creator) pairs. We may end up with duplicate (asset_id, creator) pairs during indexing, because a creator can change position. Any stale rows (older seq/slot_updated) will be ignored, meaning the API users will never see duplicate creators.

We are adding a new index on (asset_id, creator, verified) for getAssetsByCreator.

Testing

Running in Helius prod