Add apiURL to chain data for verifying contracts

[tab00]

apiURL is required to be set in hardhat.config.js to be able to verify contracts on blockchain explorer web sites using hardhat-verify.

Currently I try to generate it from the blockExplorers URLs, but not all explorer URLs follow the same format.

All other data are obtainable from @wagmi/chains for setting networks and etherscan.customChains in hardhat.config.js, so it'd be great to have apiURL as the last piece of the puzzle.