[BUG][GO] Wrong interface type in generated client model when using oneof

Created by: vikashsparky

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?
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Description

With certain kind of schema having oneOf with required field, the model generated for client does not have proper syntax for interface

type NFProfile struct {
        interface{} *interface{}
}

openapi-generator version

3.0.0

OpenAPI declaration file content or url

openapi: 3.0.0

info:
  version: '1.1.2'
  title: 'Test Service'
  description: |
    Test Service.

servers:
  - url: '{apiRoot}/nfm/v1'
    variables:
      apiRoot:
        default: https://example.com

paths:
  /instances:
    get:
      summary: Retrieves a collection of Instances
      operationId: GetInstances
      tags:
        - Instances (Store)
      parameters:
        - name: limit
          in: query
          description: How many items to return at one time
          required: false
          schema:
            type: integer
      responses:
        '200':
          description: Expected response to a valid request
          content:
            application/3gppHal+json:
              schema:
                type: object
                properties:
                  profile:
                    $ref: '#/components/schemas/NFProfile'
                minProperties: 1

components:
  schemas:
    NFProfile:
      description: Information of an NF Instance discovered by the NRF
      type: object
      required:
        - nfInstanceId
      anyOf:
        - required: [ fqdn ]
        - required: [ ipv4Addresses ]
        - required: [ ipv6Addresses ]
      properties:
        nfInstanceId:
          type: string
        nfInstanceName:
          type: string
        fqdn:
          type: string
        ipv4Addresses:
          type: string
        ipv6Addresses:
          type: string

Generation Details

~/bin/openapitools/openapi-generator-cli generate -g go -o ~/test_dir/ -i test.yaml

Steps to reproduce

~/bin/openapitools/openapi-generator-cli generate -g go -o ~/test_dir/ -i test.yaml

Related issues/PRs

Suggest a fix

Should had generated something like

type NFProfile struct {
        nfProfile *interface{}
}