[BUG] [Java][Spring] Model composition does not work for string type

Created by: yklymenko

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
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Description

It is sometimes useful to have a base type which is derived from string with all constraints, refer this type using "ref" syntax and change just the description. The problem is that generation does not work correctly for the case shown below. @Size annotation will be not generated as expected.

openapi-generator version

I use 5.0.0-beta2 in my test

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  description: test
  version: 1.0.0
  title: OpenAPI Petstore
  license:
    name: Apache-2.0
    url: 'https://www.apache.org/licenses/LICENSE-2.0.html'
paths:
  /pet:
    post:
      description: ''
      responses:
        '200':
          description: successful operation
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Pet'
components:
  schemas:
    Pet:
      title: a Pet
      description: A pet for sale in the pet store
      type: object
      properties:
        test1:
          allOf:
            - $ref: '#/components/schemas/StringMinMax'
            - description: "Property one description"
        test2:
          allOf:
            - $ref: '#/components/schemas/StringMinMax'
            - description: "Property two description"
    StringMinMax:
      type: string 
      minLength: 1
      maxLength: 5

Generation Details

java -jar openapi-generator-cli-5.0.0-beta2.jar generate -i petstore.yaml -g spring

Steps to reproduce

Generate classes
Look inside Pet class. Size annotations are missing on getters