Extend the migration tool to nft.storage

[prodalex]

Once nft.storage switches off the lights end of June, we will be able to capture some users through a migration tool over to the new web3.storage. Elizabeth is open to mentioning this in the sunset email (for some tokens when renewal of her contract is due).

Task:

• Ensure that the migration tool works for nft.storage

[heyjay44]

Closing in favour of this ticket: https://github.com/w3s-project/nonpublic/issues/15