Fix #8710

This PR deprecates the default no-args constructor for ApiHandler and replaces it with a constructor requiring to provide the implementation, in order to make easier to use the generated code without modifying it

Signed-off-by: Francesco Guardiani [email protected]

PR checklist

• Read the contribution guidelines.
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  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

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