POC: MQTT topics directly in SIGNALduino

[sidey79]

• Please check if the PR fulfills these requirements

• Tests for the changes have been added / modified (needed for for bug fixes / features)
• commandref has been added / updated (needed for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Bugfix (please link issue)
• Feature enhancement
• Documentation update
• Unittest enhancement
• other

• What is the current behavior?
  (You can also link to an open issue here, if this describes the current behavior)

SIGNALduino Module can't handle MQTT Messages.

• What is the new behavior (if this is a feature change)?

SIGNALduino can be a listener to MQTT Messages via MQTT2_CLIENT or MQTT2_SERVER Devices

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

no

• Other information:

Demonstration, wie MQTT direkt in 00_SIGNALduino eingebunden werden kann über `define SIGNALduino_mqtt SIGNALduino mqtt´:

[codecov]

Codecov Report

❌ Patch coverage is 89.26554% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.32%. Comparing base (e094250) to head (084cf43).

Files with missing lines	Patch %	Lines
t/FHEM/Devices/SIGNALduino/SD_MQTT.t	92.12%	10 Missing ⚠️
FHEM/00_SIGNALduino.pm	70.83%	7 Missing ⚠️
lib/FHEM/Devices/SIGNALduino/SD_MQTT.pm	92.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1341      +/-   ##
==========================================
- Coverage   86.58%   86.32%   -0.26%     
==========================================
  Files         141      144       +3     
  Lines       10509    10694     +185     
  Branches     1700     1708       +8     
==========================================
+ Hits         9099     9232     +133     
- Misses       1409     1461      +52     
  Partials        1        1              

Flag	Coverage Δ
fhem	77.50% <58.00%> (-0.47%)	⬇️
modules	86.32% <89.26%> (-0.26%)	⬇️
perl	95.11% <92.15%> (-0.16%)	⬇️
unittests	86.32% <89.26%> (-0.26%)	⬇️

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