[Frontend] Gemma3n audio transcriptions/translations endpoint (#23735)

Signed-off-by: NickLucche <nlucches@redhat.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

vllm/model_executor/models/whisper.py

@@ -4,7 +4,7 @@
 import math
 from collections.abc import Iterable, Mapping, Sequence
 from contextlib import nullcontext
-from typing import Optional, TypedDict, Union, cast
+from typing import Literal, Optional, TypedDict, Union, cast
 
 import numpy as np
 import torch
@@ -783,8 +783,9 @@ class WhisperForConditionalGeneration(nn.Module, SupportsTranscription,
             model_config: ModelConfig,  # not needed here
             stt_config: SpeechToTextConfig,
             language: Optional[str],
-            task_type: str,
-            request_prompt: str) -> PromptType:
+            task_type: Literal["transcribe", "translate"],
+            request_prompt: str,
+            to_language: Optional[str]) -> PromptType:
         if language is None:
             raise ValueError(
                 "Language must be specified when creating the Whisper prompt")