docs: Add Text to Speech example to cognitive service overview

[mhamilton723]

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[mhamilton723]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov-commenter]

Codecov Report

Merging #1350 (a265865) into master (caf8f76) will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1350      +/-   ##
==========================================
- Coverage   84.78%   84.71%   -0.08%     
==========================================
  Files         287      287              
  Lines       14231    14231              
  Branches      732      732              
==========================================
- Hits        12066    12056      -10     
- Misses       2165     2175      +10     

Impacted Files	Coverage Δ
...crosoft/azure/synapse/ml/io/http/HTTPClients.scala	58.33% <0.00%> (-15.01%)	⬇️
.../execution/streaming/continuous/HTTPSourceV2.scala	92.08% <0.00%> (-0.72%)	⬇️
...zure/synapse/ml/stages/PartitionConsolidator.scala	95.74% <0.00%> (+2.12%)	⬆️

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