.Net: Add generic data model sample

[westey-m]

Motivation and Context

The generic data model can be used instead of a custom data model when using the vector store implementations.
 
#8986

Description

Adding a sample to show how to use the generic data model to upsert data and retrieve using custom and vice versa, to show the flexibility of the generic data model and how it is interchangeable and interoperable with a custom data model.

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 😄