[Feature Request]: Add support for resolving keyed services from dependency injection container

[dorlugasigal]

Is your request related to a problem you have?

When using .NET's keyed services, KafkaFlow's resolver doesn't provide a way to resolve services registered with keys from the dependency injection container.

Currently, we have to use a workaround by creating a temporary service provider to pre-resolve keyed services before configuring KafkaFlow, or to pass the key as a field to the implementing class. which adds unnecessary complexity and potential performance overhead to our applications:

// Create a temporary service provider to resolve keyed services
var tempServices = new ServiceCollection();
foreach (var descriptor in services) {
    tempServices.Add(descriptor);
}
using var tempProvider = tempServices.BuildServiceProvider();
var processor = tempProvider.GetKeyedService<IMessageProcessor<TInput, TOutput>>(processorKey);

Describe the solution you'd like

We'd like KafkaFlow's resolver to support resolving keyed services directly. The IDependencyResolver interface could be extended to include methods like ResolveKeyedService<T>(object key) and that would delegate to the underlying .NET dependency injection container.

For example, when configuring middleware, we'd like to be able to do something like:

middlewares.Add<GenericProcessingMiddleware<TInput, TOutput>>(resolver => 
{
    // Resolver should support getting keyed services
    return new GenericProcessingMiddleware<TInput, TOutput>(
        resolver.GetKeyedService<IMessageProcessor<TInput, TOutput>>(processorKey),
        resolver.GetKeyedService<IMessageValidator<TInput>>(processorKey),
        resolver.GetRequiredService<IProducerAccessor>(),
        // Other dependencies...
    );
});

This would align KafkaFlow's DI capabilities with the latest .NET features and enable more flexible service resolution patterns.

Are you able to help bring it to life and contribute with a Pull Request?

No

Additional context

The current workaround of creating a temporary service provider works but feels like a hack and could lead to potential issues with scoped services or memory leaks if not managed carefully.

I would love to implement it myself by im not familiar with different types of di like Unity and such