Update to Bullseye Docker-base & Debian-maintained Broker libs

[0snap]

📔 Description

Update Docker base image and use Debian-maintained Broker libraries for communicating with Zeek.

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/threatbus, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

docker build . -t foo
docker run foo

[lava]

I tested locally that the dockerfile builds; the rest should be covered by tests.