Migrate to new tribufu project structure

Source/Tribufu.Configuration/Extensions/IConfigurationExtensions.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Tribufu. All Rights Reserved.
+// SPDX-License-Identifier: MIT
+
+using Microsoft.Extensions.Configuration;
+
+namespace Tribufu.Configuration.Extensions
+{
+    public static class IConfigurationExtensions
+    {
+        public static string? Get(this IConfiguration configuration, string prefix, string key)
+        {
+            var section = configuration.GetSection(prefix);
+            return !section.Exists() ? configuration[$"{prefix}_{key}"] : section[key];
+        }
+    }
+}