.Net: Add support for Guid and ObjectID keys in the MongoDB Connector

[damieng]

Motivation and Context

The MongoDB connector currently only supports string key types.

Description

Adds support for Guid and ObjectId key types to the MongoDB Connector.

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 😄

[westey-m]

@damieng, looks like there's still one unit test failing:

  Failed SemanticKernel.Connectors.MongoDB.UnitTests.MongoVectorStoreTests.GetCollectionWithNotSupportedKeyThrowsException [89 ms]
  Error Message:
   Assert.Throws() Failure: No exception was thrown
Expected: typeof(System.NotSupportedException)
  Stack Trace:
     at SemanticKernel.Connectors.MongoDB.UnitTests.MongoVectorStoreTests.GetCollectionWithNotSupportedKeyThrowsException() in /home/runner/work/semantic-kernel/semantic-kernel/dotnet/test/VectorData/MongoDB.UnitTests/MongoVectorStoreTests.cs:line 29
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)```