DOC: installation: add debian 11 bullseye
DOC: installation: add debian 11 bullseye

Debian 11 Bullseye deb repository exists now, add it to supported OS
versions

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