Make the class LokiHttpClient abstract to be used in appsettings.json

src/Serilog.Sinks.Loki/DefaultLokiHttpClient.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Serilog.Sinks.Loki
+{
+  public class DefaultLokiHttpClient : LokiHttpClient
+  {
+  }
+}

src/Serilog.Sinks.Loki/LokiHttpClient.cs

@@ -7,7 +7,7 @@
 
 namespace Serilog.Sinks.Loki
 {
-    public class LokiHttpClient : IHttpClient
+    public abstract class LokiHttpClient : IHttpClient
     {
         protected readonly HttpClient HttpClient;
 

src/Serilog.Sinks.Loki/LokiSinkExtensions.cs

@@ -13,7 +13,7 @@ private static LoggerConfiguration LokiHttpImpl(this LoggerSinkConfiguration sin
         {
             var formatter = logLabelProvider != null ? new LokiBatchFormatter(logLabelProvider.GetLabels()) : new LokiBatchFormatter();
 
-            var client = httpClient ?? new LokiHttpClient();
+            var client = httpClient ?? new DefaultLokiHttpClient();
             if (client is LokiHttpClient c)
             {
                 c.SetAuthCredentials(credentials);