Look for a submodule is a series of packages, e.g. ".pagetype_plugins" in all INSTALLED_APPS.

def import_apps_submodule(submodule):
    """
    Look for a submodule is a series of packages, e.g. ".pagetype_plugins" in all INSTALLED_APPS.
    """
    found_apps = []
    for appconfig in apps.get_app_configs():
        app = appconfig.name
        if import_module_or_none('{0}.{1}'.format(app, submodule)) is not None:
            found_apps.append(app)

    return found_apps