[BUG] Generator is merging nested models

Description

When multiple nested models have identical contents, the generator automatically merges them and generates only one model. This is not expected because these models are unrelated. Need an option to disable merging.

openapi-generator version

4.0.0-beta2

OpenAPI declaration file content or url

definitions:
  outer1:
    type: object
    properties:
      inner1:
        type: object
        properties:
          foo:
            type: string
  outer2:
    type: object
    properties:
      inner2:
        type: object
        properties:
          foo:
            type: string

Command line used for generation

java -jar openapi-generator-cli-4.0.0-beta2.jar generate -i api.yaml -g jaxrs-spec

Steps to reproduce

Generate code. Inner1 is generated as Outer1Inner1, but inner2 is not being generated. Outer2 now has a field Outer1Inner1 inner2, which is not expected.
This issue not language-specific.

Start by reproducing the issue with the supplied api.yaml definitions and the openapi-generator-cli command using the jaxrs-spec generator. Trace where identical nested models are merged and identify the existing option-handling path; done means an option can disable merging so both unrelated nested models are generated separately.