F null pointer list users

Summary

Add Connection::ListUsers() method

Focus

Note: currently no paging -> ListUsers always returns all known users.

Test Environment

No manual testing required.

Check List for the Author

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• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
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  • Intent of new code
  • Problems with old code
  • Why this implementation?

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• I understand the intent of this MR
• All automated tests pass
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• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
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doc/CHANGELOG.md

@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+-  Connection::ListUsers method
+
 ### Changed
 
 - Updated dependency versions.