Add missing string parameter converter

SimpleHttpServer/Types/ParameterConverters/StringParameterConverter.cs

@@ -0,0 +1,7 @@
+namespace SimpleHttpServer.Types.ParameterConverters;
+internal class StringParameterConverter : IParameterConverter {
+    public bool TryConvertFromString(string value, out object result) {
+        result = value;
+        return true;
+    }
+}