add a max lenght for username

srcs/requirements/svelte/api_front/src/pages/profile/ProfileSettings.svelte

@@ -51,7 +51,7 @@
 		.then((response) => {
 			if (!response.ok) {
 				success.username = ''
-				errors.username = "Use [a-zA-Z0-9] and - _ .";
+				errors.username = "Max length : 50 . Use [a-zA-Z0-9] and - _ .";
 				if (response.status === 409) {
 					errors.username = `${set.username} is already in use, pick a different one.`;
 				}