.Net - Fix Assistant type conversion for function calling (#5707)

### Motivation and Context

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- Fix to specify function types propertly
- Add support for ability to list agents.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

I experienced both issues and also worked with community who has also
experienced / identified both.


https://datatracker.ietf.org/doc/html/draft-bhutton-json-schema-00#section-4.2.1

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Mark Wallace <127216156+markwallace-microsoft@users.noreply.github.com>

dotnet/samples/KernelSyntaxExamples/Plugins/MenuPlugin.cs

@@ -7,6 +7,9 @@ namespace Plugins;
 
 public sealed class MenuPlugin
 {
+    /// <summary>
+    /// Returns a mock item menu.
+    /// </summary>
     [KernelFunction, Description("Provides a list of specials from the menu.")]
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1024:Use properties where appropriate", Justification = "Too smart")]
     public string GetSpecials()
@@ -18,11 +21,27 @@ public string GetSpecials()
 ";
     }
 
+    /// <summary>
+    /// Returns a mock item price.
+    /// </summary>
     [KernelFunction, Description("Provides the price of the requested menu item.")]
     public string GetItemPrice(
-        [Description("The name of the menu item.")]
+            [Description("The name of the menu item.")]
             string menuItem)
     {
         return "$9.99";
     }
+
+    /// <summary>
+    /// An item is 86'd when the kitchen cannot serve due to running out of ingredients.
+    /// </summary>
+    [KernelFunction, Description("Returns true if the kitchen has ran out of the item.")]
+    public bool IsItem86d(
+            [Description("The name of the menu item.")]
+            string menuItem,
+            [Description("The number of items requested.")]
+            int count)
+    {
+        return count < 3;
+    }
 }

dotnet/src/Experimental/Agents/AgentBuilder.cs

@@ -310,4 +310,50 @@ public AgentBuilder WithFiles(params string[] fileIds)
 
         return this;
     }
+
+    /// <summary>
+    /// Retrieve defined agents from an Azure OpenAI endpoint.
+    /// </summary>
+    /// <remarks>
+    /// The <see cref="AgentReference.Id"/> can be used to retrieve a hydrated agent via <see cref="GetAsync(string, CancellationToken)"/>/
+    /// </remarks>
+    public static async Task<IList<AgentReference>> GetAzureOpenAIAgentsAsync(string endpoint, string apiKey, string? version = null)
+    {
+        endpoint = $"{endpoint}/openai";
+        version ??= "2024-02-15-preview";
+
+        var context = new OpenAIRestContext(endpoint!, apiKey, version);
+        var result = await context.ListAssistantModelsAsync().ConfigureAwait(false);
+
+        return
+           result.Select(
+               m =>
+                   new AgentReference()
+                   {
+                       Id = m.Id,
+                       Name = m.Name
+                   }).ToArray();
+    }
+
+    /// <summary>
+    /// Retrieve defined agents from OpenAI services.
+    /// </summary>
+    /// <remarks>
+    /// The <see cref="AgentReference.Id"/> can be used to retrieve a hydrated agent via <see cref="GetAsync(string, CancellationToken)"/>/
+    /// </remarks>
+    public static async Task<IList<AgentReference>> GetOpenAIAgentsAsync(string apiKey)
+    {
+        var context = new OpenAIRestContext(OpenAIBaseUrl, apiKey);
+
+        var result = await context.ListAssistantModelsAsync().ConfigureAwait(false);
+
+        return
+            result.Select(
+                m =>
+                    new AgentReference()
+                    {
+                        Id = m.Id,
+                        Name = m.Name
+                    }).ToArray();
+    }
 }

dotnet/src/Experimental/Agents/AgentReference.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.SemanticKernel.Experimental.Agents;
+
+/// <summary>
+/// Response from agent when called as a <see cref="KernelFunction"/>.
+/// </summary>
+public class AgentReference
+{
+    /// <summary>
+    /// The agent identifier (which can be referenced in API endpoints).
+    /// </summary>
+    public string Id { get; internal set; } = string.Empty;
+
+    /// <summary>
+    /// Name of the agent
+    /// </summary>
+    public string? Name { get; internal set; }
+}

dotnet/src/Experimental/Agents/Extensions/AssistantsKernelFunctionExtensions.cs

@@ -79,11 +79,21 @@ private static string ConvertType(Type? type)
             return "number";
         }
 
+        if (type == typeof(bool))
+        {
+            return "boolean";
+        }
+
         if (type.IsEnum)
         {
             return "enum";
         }
 
-        return type.Name;
+        if (type.IsArray)
+        {
+            return "array";
+        }
+
+        return "object";
     }
 }