Adjust fallback log levels
The default mode would be more useful if it issued warnings for changes to fallbacks in the whitelist, and logged (almost) everything else at info level. Then people can make the default log level warning to focus on the most important messages.
The check_existing mode would be more useful if it only logged warning and info messages for relays
fingerprints in the existing list. It would also be more useful if it logged a warning message when a fallback in the existing list is missing from OnionOO.