[BUG][C++][Pistache][Restbed] Array of objects does not generate model file

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

Actual:
When declaring array of objects (which have properties), model is not generated.
It will result in Object.h include missing for cpp-restbed-server and cpp-pistache-server

Expected:
model/ProblematicArrayType.h (and .cpp) are created

openapi-generator version

4.0.2

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  description: Some description
  version: 0.0.1
  title: Some title

tags:
  - name: hello

paths:
  "/there":
    get:
      operationId: helloThereGet
      tags:
        - hello
      summary: Do something
      responses:
        200:
          description: Successful operation
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/ProblematicArrayType"
servers:
  - url: http://localhost:8080
components:
  schemas:
    ProblematicArrayType:
      type: array
      items:
        type: object
        properties:
          someint:
            type: integer
            format: int32
          somestring:
            type: string

Command line used for generation

openapi-generator-cli generate -i problem.yaml -g cpp-pistache-server -o generated_pistache
openapi-generator-cli generate -i problem.yaml -g cpp-restbed-server -o generated_restbed

Steps to reproduce

openapi-generator-cli generate -i problem.yaml -g cpp-pistache-server -o generated_pistache
cd generated_pistache
mkdir build
cd build
cmake ..
make -j4

Related issues/PRs

#2769 #1827 #1637

Suggest a fix

No idea how to fix it, but the issue happens both on Pistache and Restbed

Start by running the supplied OpenAPI declaration with both cpp-pistache-server and cpp-restbed-server, then inspect the generated output and build failure. The fix is complete when model/ProblematicArrayType.h and .cpp are generated for the array-of-objects schema and both generated projects build successfully with CMake and make.