Allow registering multiple Kafka health checks.

[mitchdenny]

What would you like to be added:

Currently the AddKafka results in a singleton of the KafkaHealthCheckOptions being registered with DI:

AspNetCore.Diagnostics.HealthChecks/src/HealthChecks.Kafka/DependencyInjection/KafkaHealthCheckBuilderExtensions.cs

Line 38 in 116a4ea

builder.Services.AddSingleton(_ => new KafkaHealthCheck(new KafkaHealthCheckOptions { Configuration = config, Topic = topic }));

This should be adjusted to be more like the other health checks so that multiple health checks can be registered.

Why is this needed:

If you register multiple health checks they all end up having the same options which isn't very useful. I ran into this whilst adding support for Kafka health checks in the .NET Aspire application model and I was scratching my head as to why one of my Kafka health checks wasn't returning healthy - until I figured out it was looking at the write Kafka instance (which wasn't running yet). See:

dotnet/aspire#5719