fix: valid username lowercase (#42172)

* fix: valid username lowercase

* test: add test in the validate for reject uppercase characters

* test: add test in the cypress for check on uppercase characters and reject it.

client/src/components/settings/Username.js

@@ -98,7 +98,7 @@ class UsernameSettings extends Component {
   handleChange(e) {
     e.preventDefault();
     const { username, validateUsername } = this.props;
-    const newValue = e.target.value.toLowerCase();
+    const newValue = e.target.value;
     return this.setState(
       {
         formValue: newValue,