Enable cross-chain NFT transfers on asset-hub (#2796)

This PR introduces the following changes:

- [x] Adds a `UniquesTransactor` to asset-hub-rococo
- [x] Adds a `UniquesTransactor` to asset-hub-westend

We can't add a transactor for `pallet-nfts` like we do for
`pallet-uniques` because `pallet-nfts` uses `nonfungibles_v2::Mutate`
instead of `nonfungibles::Mutate`, and making that work would be out of
scope of this PR.

With these modifications, reserve-based NFT cross-chain transfers can be
performed on asset-hub.

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

cumulus/parachains/common/src/lib.rs

@@ -67,6 +67,12 @@ mod types {
 
 	// Id used for identifying assets.
 	pub type AssetIdForTrustBackedAssets = u32;
+
+	// Id used for identifying non-fungible collections.
+	pub type CollectionId = u32;
+
+	// Id used for identifying non-fungible items.
+	pub type ItemId = u32;
 }
 
 /// Common constants of parachains.