fix: asset-registry metadata migration

[sander2]

Addresses #894 .

Note that as discussed in the issue, the migration only works if Metadata.location is None or Some(VersionedMultiLocation::V1(_)). Any metadata items that are Some(VersionedMultiLocation::V0()) will be set to None.

[xlc]

Kind of blocked by paritytech/polkadot#6884 which changes the encoding format for versioned types.

[xlc]

Actually there is no need of migration for V1 because V1 and V2 are identical (after paritytech/polkadot#6884 is merged)

[sander2]

Actually there is no need of migration for V1 because V1 and V2 are identical (after paritytech/polkadot#6884 is merged)

Nice, once that is backported this won't be required indeed, so closing this

[sander2]

Actually maybe we should still merge this to for v0 users? Better to remove the location as done by this migration, than to have invalid storage items I think

[xlc]

I am not sure if that makes sense. They should just upgrade it to the v1 format before upgrade to v3. Delete data and have invalid data is somewhat the same to the runtime as failed decode should just give the default data.