Add ASR interim results support in Assistant model and API

- Introduced `asr_interim_enabled` field in the Assistant model to control interim ASR results.
- Updated AssistantBase and AssistantUpdate schemas to include the new field.
- Modified the database schema to add the `asr_interim_enabled` column.
- Enhanced runtime metadata to reflect interim ASR settings.
- Updated API endpoints and tests to validate the new functionality.
- Adjusted documentation to include details about interim ASR results configuration.

engine/runtime/ports/asr.py

@@ -22,6 +22,7 @@ class ASRServiceSpec:
     api_key: Optional[str] = None
     api_url: Optional[str] = None
     model: Optional[str] = None
+    enable_interim: bool = False
     interim_interval_ms: int = 500
     min_audio_for_interim_ms: int = 300
     on_transcript: Optional[TranscriptCallback] = None