docs: Update SpeakerDiarizationConfig documentation.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/Speech/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
0.29.1: Pulling from googleapis/artman
Digest: sha256:b2a73f4dda03ef8fcaa973e3ba26d0cf34091f6c22c70add663af325931aef4d
Status: Image is up to date for googleapis/artman:0.29.1
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/speech/artman_speech_v1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-speech-v1.
synthtool > Running generator for google/cloud/speech/artman_speech_v1p1beta1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-speech-v1p1beta1.
synthtool > Replaced 'Copyright \\d{4}' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1p1beta1/SpeechClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/SpeechClientExtensionTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/SpeechClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/System/V1p1beta1/SpeechSmokeTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/System/V1/SpeechSmokeTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Snippet/V1/SpeechClientTest.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1p1beta1/StreamingRecognizeResponse_SpeechEventType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1p1beta1/RecognitionMetadata_MicrophoneDistance.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1p1beta1/RecognitionMetadata_InteractionType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1p1beta1/RecognitionMetadata_RecordingDeviceType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1p1beta1/RecognitionConfig_AudioEncoding.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1p1beta1/RecognitionMetadata_OriginalMediaType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/StreamingRecognizeResponse_SpeechEventType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/RecognitionMetadata_MicrophoneDistance.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/RecognitionMetadata_InteractionType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/RecognitionMetadata_RecordingDeviceType.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/RecognitionConfig_AudioEncoding.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/RecognitionMetadata_OriginalMediaType.php.
synthtool > Replaced 'new SpeechClient' in src/V1/Gapic/SpeechGapicClient.php.
synthtool > Replaced '= AudioEncoding::' in src/V1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new RecognitionConfig' in src/V1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new RecognitionAudio' in src/V1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new StreamingRecognizeRequest' in src/V1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new SpeechClient' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Replaced '= AudioEncoding::' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new RecognitionConfig' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new RecognitionAudio' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Replaced 'new StreamingRecognizeRequest' in src/V1p1beta1/Gapic/SpeechGapicClient.php.
synthtool > Cleaned up 1 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

Merging #2144 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2144   +/-   ##
=========================================
  Coverage     92.52%   92.52%           
  Complexity     4430     4430           
=========================================
  Files           305      305           
  Lines         13157    13157           
=========================================
  Hits          12173    12173           
  Misses          984      984

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