Updated entity class name to domain type to follow spring conventions

[kushagraThapar]

• Updated entity class name to domain type to follow spring conventions
• Addresses this: https://github.com/microsoft/spring-data-cosmosdb/issues/493

[codecov-io]

Codecov Report

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  Hits              ?     1269           
  Misses            ?      391           
  Partials          ?       82

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