Issue: #6268 add default values support to Avro schema generator with related test cases

[aghajani]

Resolving #6268: Adding the support to fill default attribute in generated AVRO files using avro-schema generator

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.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  • File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request. Asking for review @sgadouar @wing328

[wing328]

thanks for the PR. is there any command to validate the output?

what about adding a github workflow to do that?

ref: https://github.com/OpenAPITools/openapi-generator/tree/master/.github/workflows