[Server] Fix Shutdown Delay when registration is enabled no LDS is present.

[romanett]

Proposed changes

The server no remembers if a registration with a LDS was done and only tries to unregister on shutdown if this is the case.
This mitigates the shutdown delay when no LDS is present on the network.

Benchmark:

Test Runtime for Server Shutdown Test decreased from >10s to <2s

Related Issues

• Fixes Server shutdown delay when LDS local registration is enabled but LDS not present #2422

Types of changes

• 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.

Further comments

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 54.64%. Comparing base (884ddf3) to head (11246a8).
Report is 8 commits behind head on master.

Files	Patch %	Lines
Libraries/Opc.Ua.Server/Server/StandardServer.cs	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2589      +/-   ##
==========================================
- Coverage   54.70%   54.64%   -0.07%     
==========================================
  Files         342      342              
  Lines       65041    65059      +18     
  Branches    13331    13335       +4     
==========================================
- Hits        35581    35549      -32     
- Misses      25612    25637      +25     
- Partials     3848     3873      +25     

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