Add Support for Sepolia Ethereum Testnet

[Narlokk]

Hi,

I've been using the Rainbow Bridge and greatly appreciate the interoperability it offers between Ethereum and Aurora. Currently, the Rainbow Bridge is primarily supporting the Goerli Ethereum testnet.

However, it's extremely hard to acquire testnet ETH on Goerli. Furthermore, the Goerli testnet will be shutting down in approximately 6 months. As an alternative, the Sepolia Ethereum testnet provides a more straightforward process for developers to obtain testnet ETH for development and testing purposes.

Therefore, I would like to propose adding support for the Sepolia Ethereum testnet to the Rainbow Bridge. This change would:

• Provide an easier way for developers to obtain and use testnet ETH.
• Ensure the continued functionality and usefulness of the Rainbow Bridge even after the shutdown of the Goerli testnet.

I believe this change could greatly benefit the developer community and help maintain the overall health and user experience of the Rainbow Bridge.

Thank you for considering this request. I'm looking forward to hearing your thoughts.