RegisterParams return ERC-20 token address for payment

[pikonha]

Feature Request

The registering of a subdomain shouldn't be enforced by the standard to be paid in ETH because this makes the implementation too strict. We should instead support ERC-20 payments when applicable or ETH as established by the EIP-7528.

Describe Preferred Solution

RegisterParams should return an ERC-20 contract address when applicable or 0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee when ETH is the token used on payments as described by the EIP-7528.

Architecture Diagram

QA Replication steps

1. call registerParams
2. receive an ERC-20 contract address and use it to pay for the subdomain registering