Add support for auto-discovery of tokens via the HydraDX assetRegistry

[alecdwm]

HydraDX (and their Kusama chain, Basilisk) have built a great assetRegistry pallet which can be queried to know about all of the tokens deployed on their parachains.

At the moment, to support their tokens we have to manually copy the information from this pallet into our chaindata config and keep it up to date.

It would be much better if we could have our balance modules automatically parse the information available in their assetRegistry pallets via some sort of token auto-discovery.

The solution to this will be a useful pattern to then implement for other parachains which have some sort of asset autodiscovery capability,