feat: allow for registry override

[bee344]

Description

Updated parseRegistry to allow for overriding entries of the existing registry. This is achieved by adding the optional property overridingRegistry to AssetTransferApiOpts. Now propertyIterator takes an extra optional argument override, a boolean that defines whether we intend to override the registry or not. This value is set on parseRegistry and depends on the presence of the property overridingRegistry in the opts passed to the function. If the chainId passed in overridingRegistry is not present in the registry, it just adds it as if it were an injectedRegistry. If both options are present, it first updates the registry with injectedRegistry and then makes the changes as per overridingRegistry.

[marshacb]

minor nit. LGTM

[TarikGul]

Overall looks amazing! Small nit, I think we should change the name to overrideRegistry. In addition to that we need to update the docs in the README.md that go over the AssetTransferApiOpts.

[TarikGul]

LGTM, great job :)

[Polkadot-Forum]

This pull request has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/parity-tech-update-for-february/6630/1