[Server] Solution to USDT (ERC-20) donation

[robertu7]

(TBC) Requirements

• API to verify & record ERC-20 donations to DB;
• API to query ERC-20 donations from DB or on-chain;

Tasks

• [ ] Design API schema based on requirements;
  • revise payTo or add a new mutation?
  • revise User.wallet.transactions?
• [ ] Output to a Notion documentation;