Fix: ConnectionRefusedError on startup when no broker is running

[Kraemii]

What:
Notus-scanner exits now with a log message instead of an exception
SC-650

Why:
In case no MQTT broker was running, the notus-scanner would end with a ConnectionRefuseError as a exception. Now a log message is printed instead

How:
Start notus-scanner without having a MQTT broker running

Checklist:

• Tests
• CHANGELOG Entry
• Documentation

[codecov]

Codecov Report

Merging #247 (9056b2b) into main (8c7aad2) will not change coverage.
The diff coverage is 0.00%.

❗ Current head 9056b2b differs from pull request most recent head 340dbd2. Consider uploading reports for the commit 340dbd2 to get more accurate results

@@           Coverage Diff           @@
##             main     #247   +/-   ##
=======================================
  Coverage   70.52%   70.52%           
=======================================
  Files          25       25           
  Lines        1096     1096           
  Branches      141      141           
=======================================
  Hits          773      773           
  Misses        302      302           
  Partials       21       21           

Impacted Files	Coverage Δ
notus/scanner/daemon.py	0.00% <0.00%> (ø)

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