[kotlin-spring] kotlin-builder support

Created by: frecco75

This PR adds the support of KotlinBuilder (See https://github.com/Pozo/mapstruct-kotlin). @KotlinBuilder is interesting when we share models with java projects, because each annotated class will have a corresponding Builder class.

With this PR, each generated model will be annotated with @KotlinBuilder.

Given the schema

openapi: "3.0.1"
info:
  version: 1.0.0
  title: Users

paths:
  /users:
    get:
      responses:
        200:
          description: users
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/User'

components:
  schemas:
    User:
      type: object
      required:
        - name
      properties:
        name:
          type: string

When we compile with the option kotlinBuilder=true it generates

@KotlinBuilder data class User(
    @ApiModelProperty(example = "null", required = true, value = "")
    @field:JsonProperty("name", required = true) val name: kotlin.String
)

Note : for the moment the Lombok compiler plugin doesn't support @Builder, so this library is useful