feat: [Dialogflow] speech activity event is configurable through InputAudioConfig.enable_voice_activity_events (#9302)

* feat: speech activity event is configurable through InputAudioConfig.enable_voice_activity_events
feat: StreamingRecognitionResult now has new MessageType: DTMF_DIGITS, PARTIAL_DTMF_DIGITS, SPEECH_ACTIVITY_BEGIN, SPEECH_ACTIVITY_END
feat: ces_debug_info is available in SearchKnowledgeDebugInfo

PiperOrigin-RevId: 938734624

Source-Link: googleapis/googleapis@8a2919c

Source-Link: googleapis/googleapis-gen@06d2439
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Author: gcf-owl-bot[bot]