Made .showembed always output lowercase field names and no null values

src/NadekoBot/Modules/Searches/Common/LowerCaseNamingPolicy.cs

@@ -0,0 +1,12 @@
+using System.Text.Json;
+
+namespace SystemTextJsonSamples
+{
+    public class LowerCaseNamingPolicy : JsonNamingPolicy
+    {
+        public static LowerCaseNamingPolicy Default = new LowerCaseNamingPolicy();
+        
+        public override string ConvertName(string name) =>
+            name.ToLower();
+    }
+}