Strip leading @ from password reset input

app/soapbox/utils/input.ts

@@ -0,0 +1,13 @@
+/** Trim the username and strip the leading @. */
+const normalizeUsername = (username: string): string => {
+  const trimmed = username.trim();
+  if (trimmed[0] === '@') {
+    return trimmed.slice(1);
+  } else {
+    return trimmed;
+  }
+};
+
+export {
+  normalizeUsername,
+};