[csharp-netcore][generichost] Added OrDefault method

[devhl-labs]

Adds an OrDefault operation. If the request is not critical, the user can call this method and just ignore any errors. The error will still get logged by the none default operation.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
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  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
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  ./bin/utils/ensure-up-to-date
  

  Commit all changed files.
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