F reference field

Summary

Add a "Converter" that makes sure provided ids are valid

Focus

unit tests and implemented function

Test Environment

unittests

Check List for the Author

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• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?

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CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased] ##
 
 ### Added ###
-- check_reference_field function to check whether entities with provided ids 
+- `check_reference_field` function to check whether entities with provided ids
   exits (for example when importing data from a table)
 
 ### Changed ###