code: def list_available_backend_types() -> List[BackendType]:
      available_backend_types = []
      for (
          configurator_class
      ) in _BACKEND_TYPE_TO_CONFIGURATOR_CLASS_MAP.values():
          available_backend_types.append(configurator_class.TYPE)
      return available_backend_types
  
imports: import asyncio
  import heapq
  import time
  from typing import List, Optional, Tuple, Type, Union
  from sqlalchemy import delete, update
  from sqlalchemy.ext.asyncio import AsyncSession
  from dstack._internal.core.backends.base import Backend
  from dstack._internal.core.backends.local import LocalBackend
  from dstack._internal.core.errors import BackendInvalidCredentialsError, BackendNotAvailable, ResourceExistsError, ServerClientError
  from dstack._internal.core.models.backends import AnyConfigInfoWithCreds, AnyConfigInfoWithCredsPartial, AnyConfigValues
  from dstack._internal.core.models.backends.base import BackendType
  from dstack._internal.core.models.instances import InstanceAvailability, InstanceOfferWithAvailability
  from dstack._internal.core.models.runs import Job
  from dstack._internal.server.models import BackendModel, ProjectModel
  from dstack._internal.server.services.backends.configurators.base import Configurator
  from dstack._internal.server.settings import LOCAL_BACKEND_ENABLED
  from dstack._internal.server.utils.common import run_async
  from dstack._internal.utils.logging import get_logger
label_desc: Use image node_id 3 for calling a global function with example usage: list_available_backend_types() and returns: available_backend_types