Add to Hardhat page in the Filecoin Docs - adding Calibration and Mainnet as custom networks

[eshon]

Plesae add a note about how to add Calibration and Mainnet as a custom network to HardHat on this Filecoin Docs x HardHat page and provide the JSON snippet devs need:

https://docs.filecoin.io/smart-contracts/developing-contracts/hardhat

[nijoe1]

I think we can close this issue after PR #2409 gets merged.

• The above PR includes instructions on how to set up hardhat custom networks for Blockscout and Sourcify contract verification
• The fevm-hardhat-kit, which is the main focus of the hardhat page, was updated and now it supports contract verification by default.