ENH: impmlement handling of environment variables
ENH: impmlement handling of environment variables

See also IEP01
(https://lists.cert.at/pipermail/intelmq-dev/2020-December/000344.html)
which states that "Every bot also consults the environment and the
values that are set there overwrite the values in any configuration
file"

aaronkaplan/intelmq,aaronkaplan/intelmq,aaronkaplan/intelmq,certtools/intelmq,certtools/intelmq,certtools/intelmq