ASN Lookup expert: create missing database file #2682

Hello all, during a recent update i got confused slightly by the behavior of the asn_lookup expert:

• in a custom script we run before starting intelmq, we check whether the database file exists. If it doesnt we run intelmq.bots.experts.asn_lookup.expert --update-database as advised in the docs
• but the command fails with:

... /intelmq/bots/experts/asn_lookup/expert.py", line 127, in update_database
    raise ValueError('Database file does not exist or is not a file.')
ValueError: Database file does not exist or is not a file.

Bot 'asn-lookup-expert': File given as parameter 'database' (/var/lib/intelmq/bots/asn_lookup/ipasn.dat) does not exist. You may need to trigger first downloading manually. See: https://docs.intelmq.org/latest/user/bots/#asn-lookup.

My question is why not make the bot download the fresh database if it's missing - everything seems to be ready for it in the bot's code. I can submit a PR if this is agreed upon.

Otherwise, the linked docs could be improved with an explanation on why we need to do the initial download manually.

Cheers.