Testing the fork config file using migration's checkpoint file

[ghost-not-in-the-shell]

Once we fully migrated a network from compatible branch to berkeley's archive database, we get a side product which is the replayer's checkpoint file at the very end of the migration. This checkpoint file contains the ledger up till the fork block (in json format). If we can somehow convert the receipt_chain_hash of each account in the checkpoint file to be the same as the one we use for fork config file (which is just the receipt_chain_hash of mainnet but in berkeley format). Then the ledger_hash of this checkpoint file should be the same as the genesis ledger hash for the new network.

This helps to verify that the fork config file we get from the state export tool is right.