[BUG][JAVA] jersey2 generated code for `oneOf` doesn't support nested bean validation

Bug Report Checklist

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

Description

When using oneOf complex types, it appears that bean validation isn't run on the inner objects for the oneOf. The root cause being the generated models don't annotate with @Valid annotation.

openapi-generator version

latest.release

OpenAPI declaration file content or url

Type1:
  title: Type1
  type: object
  properties:
    type:
      type: string
      default: Type1
    reasonCode:
      type: string
   required:
   - reasonCode
   - type

Type2:
  title: Type2
  type: object
  properties:
    type:
      type: string
      default: Type2
    reasonCode:
      type: string
   required:
   - reasonCode
   - type

RequestInfoChoice:
  title: RequestInfoChoice
  oneOf:
    - $ref: '#/Type1'
    - $ref: '#/Type2'
  discriminator:
    propertyName: type
  required:
    - type

Generation Details

Leveraging gradle plugin with this config

openApiGenerate {
    generatorName = "java"
    library = "jersey2"
    inputSpec = "$projectDir/***.yaml".toString()
    outputDir = "$buildDir/generated".toString()
    apiPackage = "*****"
    modelPackage = "*****"
    additionalProperties = [
        useOneOfDiscriminatorLookup: "true"
    ]
    configOptions = [
        serializationLibrary: "jackson",
        performBeanValidation: "true",
        useBeanValidation: "true",
        legacyDiscriminatorBehavior: "false",
        dateLibrary: "java8",
        hideGenerationTimestamp: "true",
    ]
}

Steps to reproduce

1. Generate Code
2. Create an empty RequestInfoChoice like so

RequestInfoChoice request = new RequestInfoChoice();
Type1 type = new Type1();
request.setActualInstance(type1)

3. Invoke javax.validation on model

ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
javax.validation.Validator validator = factory.getValidator();

Set<ConstraintViolation<T>> violations = validator.validate(request);
Assert.assertFalse(violations.isEmpty()) <--- this is returning true when there should be a validation error.

Suggest a fix

I believe we should annotate the get methods on AbstractOpenApiSchema.java with @Valid to ensure nested validation is performed. here: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/Java/libraries/jersey2/AbstractOpenApiSchema.mustache#L46

Start with modules/openapi-generator/src/main/resources/Java/libraries/jersey2/AbstractOpenApiSchema.mustache, especially the generated accessors, and reproduce the issue using the supplied oneOf schema and jersey2 configuration. Validate a generated RequestInfoChoice containing an empty Type1; done means bean validation reports the missing required fields on the nested object.