Describe the bug
When using the dimensions attribute on a IEmbeddingGenerator request, the outputted dimensions from the Vertex API call is whatever the default is for the model.

To Reproduce

        var embeddings = await embeddingGenerationService.GenerateAsync("hello",new EmbeddingGenerationOptions() {
            Dimensions = 128,
            ModelId = "gemini-embedding-001",
        }, cancellationToken);

        Console.WriteLine(embeddings.Vector.Length);

^ The above outputs: 3072 (the default for that model.)

Expected behavior
The outputted dimensions should respect the inputted value.

Platform

• Language: C#
• Source: Microsoft.SemanticKernel.Connectors.Google, 1.63.0-alpha
• AI model: Google gemini-embedding-001
• IDE: vscode
• OS: Mac

Additional context
Related:

#10488
#10489

The above previous changes look to have only added support to the Google Gemini connector, not the VertexAI connector.