Process ERC-721 information

[brunomenezes]

📄 Context

Support to the ERC721Portal will be added to the UI, and we can process events from ERC-721 Portal to save handy information to provide consistent support to the UI like we already do with ERC-20.

✔️ Solution

Index metadata about the ERC-721 token passing through the portal. Even if the name and symbol are not implemented as per Spec, we want to know that such a contract address was already used.

Option 1

Add a new Domain:
Domain Name: NFT
Cardinality: 10
Fields: [id: ID!, name: String, symbol: String]

### Option 2
Update the existing Token domain, making the fields name, symbol and decimals optional. Also, Add a field type enumerable ERC20, ERC721 for easy filtering and that specific fields will always be null e.g. ERC-721 spec as per time of writing has no decimals metadata.

EIP-721: https://eips.ethereum.org/EIPS/eip-721

📈 Subtasks

• Add ERC721 ABI.
• Index ERC-721 info for inputs coming from ERC721Portal address.
• Add test case.

🎯 Definition of Done

• Successfully index the ERC-721 token information.

[brunomenezes]

@tuler,
What do you think? I am inclined to go with option 1.

[brunomenezes]

I am moving with option 1.