Consider WriterGroups in MQTT KeepAlive calculation

[jnsjll]

Proposed changes

According to the specification, an MQTT Keep Alive value should be set that is slightly higher than the highest KeepAliveTime setting of all writer groups.

This change calculates the KeepAliveTime considering added writer groups when starting the MqttPubSubConnection.

Related Issues

• Fixes [PubSub] MQTT Keep Alive calculation does not consider WriterGroups #3227

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

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• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
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• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
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• Any dependent changes have been merged and published in downstream modules.

Further comments

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.00%. Comparing base (d25caff) to head (30c38d6).
⚠️ Report is 140 commits behind head on master.

Files with missing lines	Patch %	Lines
...es/Opc.Ua.PubSub/Transport/MqttPubSubConnection.cs	50.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3616       +/-   ##
===========================================
+ Coverage   51.86%   66.00%   +14.13%     
===========================================
  Files         370      459       +89     
  Lines       78618    97826    +19208     
  Branches    13650    16383     +2733     
===========================================
+ Hits        40779    64566    +23787     
+ Misses      33705    28192     -5513     
- Partials     4134     5068      +934     

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