add collection attribute order support

[Snepsid]

Summary

• add an attributeOrder column to collections and collections_sepolia
• expose attributeOrder through the collection preview RPCs
• use collection.attributeOrder to sort marketplace filter keys
• keep trait_count pinned last

[Snepsid]

I should probably be doing this as jsonb not text[], huh?

[Snepsid]

No, text[] looks good here, but could maybe implement the use of DEFAULT instead of NULL