Task: Add TextFormatter function to format the string with args

test/text_formatter_test.dart

@@ -0,0 +1,15 @@
+import 'package:configurable/text_formatter.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('text formatter function format', () {
+    var text1 = 'Hello, {0}!';
+    var result1 = TextFormatter(text1).format(['Sambo']);
+
+    var text2 = 'Hello, {name}!';
+    var result2 = TextFormatter(text2).decorate({'name': 'Chea'});
+
+    expect('Hello, Sambo!', result1);
+    expect('Hello, Chea!', result2);
+  });
+}