.Net: AzureCosmosDBNoSQLMemoryStore GetAsync with embeddings false implementation

[atiq-bs23]

Motivation and Context

GetAsync is returning with embedding even if the withEmbedding parameter is false.

Description

Current implementation will return MemoryRecord based on withEmbedding flag.

Note

The method isn't being called yet, but I updated it because the implementation was missing.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄