[Client] select the most secure User Identity Token if a server offers multiple ones

[romanett]

Proposed changes

This fix makes the client select the most secure UserIdentity Token if a server offers more than one.
Before the client just selected the first UserIdentity Token offered by the server.

Related Issues

• Fixes OPC Foundation library doesnt select the most secured encryption algorithm to ActivateSessionRequest #2191

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 94.11765% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 54.62%. Comparing base (663ed10) to head (5fb7a7f).

Files	Patch %	Lines
...Ua.Core/Stack/Configuration/EndpointDescription.cs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2611      +/-   ##
==========================================
- Coverage   54.68%   54.62%   -0.07%     
==========================================
  Files         343      343              
  Lines       65216    65217       +1     
  Branches    13354    13354              
==========================================
- Hits        35664    35622      -42     
- Misses      25676    25712      +36     
- Partials     3876     3883       +7     

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[mregen]

minor improvements inline, please check.
imho we should also determine the best security policy by this function instead of the server supplied values in the SelectBestendpoint helper. But that could be done in separate PR.

[mregen]

nit - I wonder which stringcomparison policy is used here...

[mregen]

one typo to go...

[romanett]

Also added calculated Security Level to the Endpoint Selection