Microsoft.Extensions.Configuration support

[ReubenBond]

This PR adds support for configuring clients and silos using Microsoft.Extensions.Configuration, otherwise known as IConfiguration.

The systems is extensible: providers of known kinds (Clustering, Reminders, GrainStorage, Streaming, BroadcastChannel) can be registered using an assembly-level RegisterProvider attribute like so:

[assembly: RegisterProvider("Static", "Clustering", "Client", typeof(StaticGatewayListProviderBuilder))]

internal sealed class StaticGatewayListProviderBuilder : IProviderBuilder<IClientBuilder>
{
    public void Configure(IClientBuilder builder, string name, IConfigurationSection configurationSection)
    {
        var endpoints = new List<IPEndPoint>();
        var gatewaysSection = configurationSection.GetSection("Gateways");
        foreach (var child in gatewaysSection.GetChildren())
        {
            if (IPEndPoint.TryParse(child.Value, out var ep))
            {
                endpoints.Add(ep);
            }
        }

        builder.UseStaticClustering([.. endpoints]);
    }
}

Perhaps we could make the configuration more open-ended by allowing the "kinds" themselves to be extensible. The only non-trivial part of doing that is that we need to know when a "kind" is a singleton ("Clustering", "Reminders") vs named (the others).
 
Here is an example configuration for a server:

{
  "Orleans": {
    "Name": "MyUniqueSiloName",
    "ClusterId": "fooboo",
    "ServiceId": "testarossa",
    "Endpoints": {
      "AdvertisedIPAddress": "127.0.0.1",
      "SiloListeningEndpoint": "127.0.0.1:11111"
    },
    "Clustering": {
      "ProviderType": "Development",
      "PrimarySiloEndPoint": "127.0.0.1:11111"
    },
    "Reminders": {
      "ProviderType": "Memory"
    },
    "GrainStorage": {
      "Default": {
        "ProviderType": "Memory"
      },
      "PubSubStore": {
        "ProviderType": "Memory"
      }
    },
    "Streaming": {
      "ItemUpdates": {
        "ProviderType": "Memory"
      }
    },
    "BroadcastChannel": {
      "MyNotifications": {
        "ProviderType": "Default"
      }
    }
  }
}

Here is an example configuration for a corresponding client:

{
  "Orleans": {
    "ClusterId": "fooboo",
    "ServiceId": "testarossa",
    "Clustering": {
      "ProviderType": "Static",
      "Gateways": [ "127.0.0.1:30000" ]
    },
    "Streaming": {
      "ItemUpdates": {
        "ProviderType": "Memory"
      }
    },
    "BroadcastChannel": {
      "MyNotifications": {
        "ProviderType": "Default"
      }
    }
  }
}

TODO

• Add remaining providers
• Add configuration test coverage (TestingHost uses this now, but we can add more specific tests)

Later

• Add documentation for configuring Orleans using Microsoft.Extensions.Configuration
• Add ConfigurationSchema.json files once they're supported (currently Aspire & VS only)

Fixes #6565

Microsoft Reviewers: Open in CodeFlow

[ReubenBond]

@benjaminpetit ptal

[jdom]

This is pretty cool! :)