Create a bin/entrypoint script for Docker use

[wolf31o2]

This script should:

• Enable set -x in the script and --debug argument with DEBUG environment variable
• Detect empty Dingo database and use mithril-client to download, dingo load to load it
• Support resuming a dingo load if it didn't complete
• Validate configuration (CARDANO_CONFIG matches CARDANO_NETWORK, for example) for known networks
• Support CARDANO_NETWORK=devnet as both a block producer and client-only