fix: rococo initialization in the registry

[TarikGul]

rel: #293

This ensures that the registry can initialize with rococo as the relay chain.

Important note:

In order to use rococo's asset hub with the AssetTransferApi one will need to hardcode the specName into the initialization like the following:

new AssetTransferApi(api, `asset-hub-rococo`, xcmVersion);

The reason being, kusama's asset hub and and rococo's asset-hub both share the same specName currently and will cause conflicts. We currently do an overewrite in the registry that the api uses and set the specName for rococo's asset hub to be asset-hub-rococo. This should be resolved at a higher level in the below PR for asset-hub's spec.

rel: paritytech/polkadot-sdk#1215

[TarikGul]

Im running into one issue that I can see will be a potential bug.

The specName for rococos asset-hub is also statemine... Which would cause a conflict in lookup.