Add Sepolia to InfuraProvider

[remyroy]

Describe the Feature

Sepolia is now a supported network by Infura. Adding it to InfuraProvider as a supported network would make it easier for users to use that network with Infura.

Code Example

No response

[ricmoo]

Added in [5.7.1](release: https://github.com/ethers-io/ethers.js/releases/tag/v5.7.1).

Thanks! :)