Integrate more paymasters

[johnson86tw]

The app currently uses a default Public Paymaster, which I deployed on testnets and funded with tokens. On mainnet, we likely won’t be able to be so generous.

Current available paymasters:

• Public Paymaster
• Support USDC Paymaster #18

Below is a list of paymasters that could be considered for future integration:

• PrepaidGas: Anonymous gas payments using pooled credits, built on top of ERC-4337 Paymasters and the Semaphore protocol.
• SimplePrivacyPoolPaymaster