Add a `wETHApprovalBasedPaymaster` contract

[dutterbutter]

Paymaster Description

Objective:

To create a paymaster that facilitates the payment of transaction fees in wETH (wrapped Eth) using the ApprovalBased flow.

Functionality:

1. Paymaster Role: The paymaster should sponsor transactions for users, enabling them to pay transaction fees in wETH.
2. Approval-Based Flow: Implement the ApprovalBased paymaster flow, which requires users to set a certain allowance for the paymaster to operate. The paymaster should ensure that the provided allowance is sufficient for the transaction fees.

Rationale:

Creating a paymaster that pays fees in wETH, we can enhance user experience, security, and flexibility, promoting broader adoption of zkSync's advanced features.

Task Deliverables:

• Paymaster implementation: Develop and test the paymaster that pays fees in wETH using the ApprovalBased flow.
• Documentation: Provide detailed documentation on how the paymaster works, how to integrate it, and any prerequisites required.
• Test Cases: Implement test cases to ensure the paymaster functions as expected and handles edge cases.
• Update readme: Update the readme to reflect new example.

[Thirawat11]

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