Videointelligence synth: add support for speech transcription feature

[dpebot]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Cloning googleapis. synthtool > Running generator for google/cloud/videointelligence/artman_videointelligence_v1beta1.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/video-intelligence-v1beta1. synthtool > Running generator for google/cloud/videointelligence/artman_videointelligence_v1beta2.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/video-intelligence-v1beta2. synthtool > Running generator for google/cloud/videointelligence/artman_videointelligence_v1p1beta1.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/video-intelligence-v1p1beta1. synthtool > Running generator for google/cloud/videointelligence/artman_videointelligence_v1p2beta1.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/video-intelligence-v1p2beta1. synthtool > Running generator for google/cloud/videointelligence/artman_videointelligence_v1.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/video-intelligence-v1. synthtool > Replaced "'google-cloud-video-intelligence', \\).version" in google/cloud/videointelligence_v1beta1/gapic/video_intelligence_service_client.py. synthtool > Replaced "'google-cloud-video-intelligence', \\).version" in google/cloud/videointelligence_v1/gapic/video_intelligence_service_client.py. synthtool > Replaced "'google-cloud-video-intelligence', \\).version" in google/cloud/videointelligence_v1p1beta1/gapic/video_intelligence_service_client.py. synthtool > Replaced "'google-cloud-video-intelligence', \\).version" in google/cloud/videointelligence_v1p2beta1/gapic/video_intelligence_service_client.py. synthtool > Replaced "'google-cloud-video-intelligence', \\).version" in google/cloud/videointelligence_v1beta2/gapic/video_intelligence_service_client.py. synthtool > Cleaned up 0 temporary directories.