[BUG] [Spring] Params with provided default values should not be `Optional`s with useOptional

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

The useOptional config value wraps non-required parameters in Java Optional<>. However, if you specify a default value for that parameter, the value won't be null, so it makes it burdensome and harder to read the code if we wrap parameters that do have a default value in Optional.

openapi-generator version

Latest on master

OpenAPI declaration file content or url

This issue exists in the sample for spring-useoptional: https://github.com/OpenAPITools/openapi-generator/blob/master/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/api/FakeApi.java#L450

Generation Details

./run-in-docker.sh /gen/bin/generate-samples.sh /gen/bin/configs/spring-boot-useoptional.yaml

Steps to reproduce

• Generate code against sample with the provided spring-boot-useoptional.yaml config.
• See that testEnumParameters has a parameter with a default value but is still an Optional: @ApiParam(value = "Query parameter enum test (string)", allowableValues = "_abc, -efg, (xyz)", defaultValue = "-efg") @Valid @RequestParam(value = "enum_query_string", required = false, defaultValue = "-efg") Optional<String> enumQueryString
• I would expect the output to be: @ApiParam(value = "Query parameter enum test (string)", allowableValues = "_abc, -efg, (xyz)", defaultValue = "-efg") @Valid @RequestParam(value = "enum_query_string", required = false, defaultValue = "-efg") String enumQueryString

Related issues/PRs

Suggest a fix

I have a PR I'll link here to fix

Start with the spring-useoptional sample, especially samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/api/FakeApi.java and spring-boot-useoptional.yaml. Run ./run-in-docker.sh /gen/bin/generate-samples.sh /gen/bin/configs/spring-boot-useoptional.yaml and inspect testEnumParameters. Done means parameters with default values are generated as String rather than Optional while other useOptional behavior remains unchanged.