class_docstr: Stand-in class to replace a Flask App Builder.
  
  The only purpose is to provide the ``self.appbuilder.get_session`` interface
  for ``ApplessAirflowSecurityManager`` so it can be used without a real Flask
  app, which is slow to create.
code: def __init__(self, session: Session | None = None) -> None:
      self.get_session = session
  
imports: from __future__ import annotations
  from typing import TYPE_CHECKING
  from airflow.providers.fab.auth_manager.security_manager.override import FabAirflowSecurityManagerOverride
label_desc: Use image node_id 1 to create a new FakeAppBuilder object  with example: obj = FakeAppBuilder(session)