chore: Creating a unified mechanism to generate blocklists for ckBTC and ckETH

[THLO]

This PR adds a Python script to generate blocklists for ckBTC and ckETH based on the OFAC SDN list.

There are some differences in the produced blocklist files compared to the current files:

Differences to the current ckBTC blocklist file:

1. The new blocklist file has a comment at the beginning about the script that was used to generate it.
2. The new blocklist file has a more concise error message for the invalid Bitcoin address in the OFAC SDN list.

Differences to the current ckETH blocklist file:

1. The new blocklist file has a comment at the beginning about the script that was used to generate it, replacing the old comment.
2. Since Ethereum addresses are case-insensitive, all addresses are now consistently in lower case.
3. The parameter from_address in the function is_blocked has been changed to address to make it consistent with the corresponding function for ckBTC.

Corresponding ticket: https://dfinity.atlassian.net/browse/XC-250

[gregorydemay]

Thanks a lot @THLO for making this script! Some minor comments and python newbie questions.