Add an `ERC20gatedPaymaster` contract

[dutterbutter]

Paymaster Description

Objective: Implement an ERC20GatedPaymaster that covers gas fees for users based on their possession of a specific ERC20 token.

Functionality:

• Before agreeing to pay the gas fee, the ERC20GatedPaymaster will verify if the user holds a certain ERC20 token in their account.
• The user must have a balance greater than 0 of the specified ERC20 token to be eligible.
• If eligible, the paymaster will cover the corresponding gas fees for the user's transaction.

Rationale

1. Extended Utility for Tokens: This paymaster concept augments the utility of governance tokens and other ERC20 tokens. Token holders can engage in platform activities without the concern of gas fees.
2. Innovative Use Cases: Projects can incentivize their communities to hold onto their tokens by offering gas-free transactions.
3. Ease of Adoption: With the proliferation of ERC20 tokens in various projects, a ready-to-use ERC20GatedPaymaster can easily be adopted and integrated, making it a valuable tool for numerous projects.

Additional Information

• Extending Considerations: While the primary check is for a non-zero balance, the contract can potentially be extended to require minimum token thresholds for different tiers of gas fee coverage.

Task deliverable

• Adds ERC20GatedPaymaster contract
• Add to the UI integration
• Add unit tests
• Updates readmes

[Ayoseun]

Is this issue still opened, can you please assign it to me