[BUG][JAXRS-CXF-Client]Missing import of java.util.Objects in model classes

Created by: KiriRea

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

I've generated jaxrs-cxf-client by OpenAPI Generator CLI (6.0.1). After generate, I found all model classes have import error of "java.util.Objects;". I think all model classess should be added import of "java.util.Objects;" during generating jaxrs-cxf-client.

openapi-generator version

6.0.1

OpenAPI declaration file content or url

Any OpenAPI declaration file like below. https://editor.swagger.io/ 　File -> Convert and save as JSON

Generation Details

1. Access above link(https://editor.swagger.io/), and click "File" -> "Convert and save as JSON" (download swagger.json).
2. Generate jaxrs-cxf-client by openapi-generator-cli.jar.

java -jar openapi-generator-cli-6.0.1.jar generate -g jaxrs-cxf-client -o PetStoreSample -i swagger.json

Steps to reproduce

• After generate jaxrs-cxf-clint, check model classes.
• equals method and hashCode method have import error about java.util.Objects.

public class Category  {
    ...
    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
      Category category = (Category) o;
      return Objects.equals(id, category.id) &&
          Objects.equals(name, category.name);
    }

    @Override
    public int hashCode() {
      return Objects.hash(id, name);
    }

Related issues/PRs

None.

Suggest a fix

Automatically add "import java.util.Objects;" to each model class.