SMTP output bot: add Content-Disposition MIME header

[ghost]

The CSV attachments sent by the SMTP output bot are not recognized as CSV by MS Outlook.

Probably the SMTP output needs to add an additional MIME header to the attachment in the mail, so that Microsoft Outlook interprets the attachment as CSV-file.

So this:
Content-Disposition: attachment; filename="somefeed.csv"
needs to be added using
https://docs.python.org/3/library/email.compat32-message.html#email.message.Message.add_header
at about this place in the IntelMQ code:

intelmq/intelmq/bots/outputs/smtp/output.py

Line 69 in a512760

msg.attach(MIMEText(attachment, 'csv'))

(assumptions only, needs to be verified)