feat: Add SignatureBasedPaymaster contract

[hoshiyari420]

Paymaster Description

Objective: Implement aSignatureBasedPaymaster contract that covers gas fees for users based on valid signature provided by the signer of the paymaster contract.

Changes introduced in this PR:

• Adds SignatureBasedPaymaster contract.
• Adds unit testing for SignatureBasedPaymaster matching repository standards.
• Adds Deployment script for SignatureBasedPaymaster matching repository standards.
• Updates script commands in package.json file
• Updates readme file

Additional Information

Functionality:

• This paymaster contract shall validate based on the signature provided through innerInputs whether or not the user's transaction shall be allowed to proceed or not.
• The signer shall have authority to ensure signature is only valid upto particular timestamp.
• The signature shall be EIP712 compliance which is signed on values like (user address, last timestamp, nonces).
• Users are required to provide certain inputs such as signature and last timestamp as innerInputs in paymaster params.
• The paymaster will then check signature based on transaction.from, block.timestamp and nonces to ensure only valid users are allowed to use paymaster.

Security Considerations:

• Paymaster should use nonce for every user in validating signatures which increments on every successful transactions.
• Paymaster should check expiry timestamp of signatures.
• Paymaster should validate signatures based on transaction.from to ensure correct user has sent transaction.
• Paymaster should revert if recovered signer does not match or signature expires.
• Owner can update the paymaster signer.
• Owner should be able to cancel any user's nonce.
• EIP712 compliance signatures support.
• Use of battle-tested standard libraries for ECDSA signature verification(Openzeppelin).

[dutterbutter]

This is a great use case for paymaster usage and a fantastic external contribution. Thank you very much for the time and energy on this. 🚀 🙏

[hoshiyari420]

yay! 💫
Please do update the issue as well. #23 @dutterbutter