[Java] Use correct annotation for optional request body

[hinrik]

This adds required=false to the @RequestBody annotation when the OpenAPI
definition has the body marked as not required.

@bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608

[wing328]

Please remove the line break from the mustache templates (bodyParams.mustache) and run the following to update the Petstore samples so that the CIs can verify the change.

./bin/spring-all-petstore.sh
./bin/java-pkmst-petstore-server.sh
./bin/kotlin-springboot-petstore-all.sh

[hinrik]

Is that CircleCI failure actually related to the change?

[wing328]

Not related to this PR and we've fixed it in the latest master.

Please resolve the merge conflicts and pull the latest master into your branch.