Add dynamic ABI fetching.

[salieflewis]

I've attempted this with abi-data but run into the issue where I can't establish the ABI as a const, and therefore can't get type safety and autocomplete when using the ABI alongside wagmi.

I've never attempted this simply by supplying an Etherscan key and attempting to pull in the data that way. I'll likely wait for a type safe working example using abi-data unless someone comes in with a better approach.

[salieflewis]

I've opened up an issue surrounding this here. I'll probably need to spin up a code sandbox to more easily articulate the behavior I'm looking for.