Update MQTTnet nuget package version 3.1.1 to 4.2.1.781 (#2272)

[KneShell]

Proposed changes

Since MQTTnet 3.1.1 do not compatible with 4.X.X (current version)
I can't use MQTTnet 4.X.X in my own Opc Ua PubSub Project as nuget package.

So I update MQTTnet 3.1.1 to 4.2.781 (current version)
Change code to be compatible with MQTTnet 4.2.781 version.
And check if all test passed. (It is)

#2272 #2272

Related Issues

• Fixes Update MQTTnet nuget package version 3.1.1 to 4.2.1.781 #2272

Types of changes

What types of changes does your code introduce?

• 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

• I have read the CONTRIBUTING doc.
• I have signed the CLA.
• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
• I fixed all introduced issues with CodeQL and LGTM.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• I have added necessary documentation (if appropriate).
• Any dependent changes have been merged and published in downstream modules.

[CLAassistant]

All committers have signed the CLA.

[mregen]

Hi @KneShell , did you also test/fix the PubSub sample apps?

[mregen]

btw, nice work, thanks for your contribution. Happy to take it if all is passing.

[codecov]

Codecov Report

Merging #2273 (3a44669) into master (5f82d1b) will increase coverage by 0.10%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2273      +/-   ##
==========================================
+ Coverage   58.94%   59.05%   +0.10%     
==========================================
  Files         330      330              
  Lines       63252    63250       -2     
==========================================
+ Hits        37285    37352      +67     
+ Misses      25967    25898      -69     

Files Changed	Coverage Δ
...aries/Opc.Ua.PubSub/Transport/MqttClientCreator.cs	0.00% <0.00%> (ø)
...es/Opc.Ua.PubSub/Transport/MqttPubSubConnection.cs	29.29% <0.00%> (ø)

... and 17 files with indirect coverage changes

[mrsuciu]

Good upgrade work 👍