Allow configuring partitions and consumer groups for Aspire 8/9 event hubs emulator

Program.cs

using Aspire.Hosting.Azure;
using System.Text.Json;

var builder = DistributedApplication.CreateBuilder(args);

var eh = builder.AddAzureEventHubs("eh")
    .RunAsEmulator()
    .AddEventHub("hub1");

builder.Eventing.Subscribe<AfterEndpointsAllocatedEvent>(
    async (e, ct) =>
    {
        var emulatorResource = builder.Resources
            .OfType<AzureEventHubsResource>().Single(x => x is
            {
                IsEmulator: true
            });

        string targetPath = "/Eventhubs_Emulator/ConfigFiles/Config.json";

        var configFileMount = emulatorResource.Annotations.OfType<ContainerMountAnnotation>()
                .Single(v => v.Target == targetPath);

        var json = await File.ReadAllTextAsync(configFileMount.Source!);
        var config = JsonSerializer.Deserialize<EmulatorConfig>(json);

        var hub = config!.UserConfig.NamespaceConfig[0].Entities[0];
        
        hub.PartitionCount = "4";

        // note: do NOT add $default - it will be added automatically by the emulator
        hub.ConsumerGroups = [
            new() {  Name="foo" },
            new() { Name = "bar" }];

        await using var s = File.OpenWrite(configFileMount.Source!);
        JsonSerializer.Serialize(s, config);
    });

builder.AddProject<Projects.dummy>("console")
    .WithReference(eh);

builder.Build().Run();



public class EmulatorConfig
{
    public UserConfig UserConfig { get; set; }
}

public class UserConfig
{
    public List<NamespaceConfig> NamespaceConfig { get; set; }
    public LoggingConfig LoggingConfig { get; set; }
}

public class LoggingConfig
{
    public string Type { get; set; }
}

public class NamespaceConfig
{
    public string Type { get; set; }
    public string Name { get; set; }
    public List<Entity> Entities { get; set; }
}

public class Entity
{
    public string Name { get; set; }
    public string PartitionCount { get; set; }
    public List<ConsumerGroup> ConsumerGroups { get; set; }
}

public class ConsumerGroup
{
    public string Name { get; set; }
}

This worked perfectly for my Aspire 9 project. Many thanks!