Changes to Update Voice Agent Group

added the new optional request property agent_voice_variants

added the optional property agent_voice_variants to the response with the 200 status

added the optional property pre_pickup_prompt_segments to the response with the 200 status

added the new google enum value to the pre_pickup_variants/items/voice_provider response property for the response status 200

added the new google enum value to the pre_pickup_voice_provider/anyOf[subschema #1: PrePickupVoiceProvider] response property for the response status 200

added the new google enum value to the request property pre_pickup_variants/anyOf[subschema #1]/items/voice_provider

added the new google enum value to the request property pre_pickup_voice_provider/anyOf[subschema #1: PrePickupVoiceProvider]