Allow getContract to use the "Config" object produced by wagmi/cli for contract address

[masha256]

wagmi config has the ability to specify addresses for contracts, including per-chain addresses. It would be great if viem getContract could accept the generated "Config" object, which includes the abi, from wagmi - including the per-chain addresses, where it automatically uses the contract address that matches the chain configured in the viem client.

And of course, when the client switches chains, it should switch to the contract address for that chain.