Deprecate .NET framework 4.6.2 support, sync with samples repo

[mregen]

Proposed changes

• Deprecate support for Nuget package support of .NET Framework 4.6.2
• Bump sample applications to 4.8
• update some copyright headers / supporting files (editorconfig etc.)
• fix a few warnings
• fix an issue with SessionReconnectHandler, in certain combination of reconnect period and exponential backoff the .NET sample app never reconnected.

Related Issues

• Fixes Deprecate support for .NET Framework 4.6.2, instead only support .NET Framework 4.8 #2066

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 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

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[mrsuciu]

Looks Ok