Update userId placeholder (#2465)

* update userId placeholder

* update sample names from login username input

src/app/components/invite-user-prompt/InviteUserPrompt.tsx

@@ -194,7 +194,7 @@ export function InviteUserPrompt({ room, requestClose }: InviteUserProps) {
                       ref={inputRef}
                       onChange={handleSearchChange}
                       onKeyDown={handleKeyDown}
-                      placeholder="@john:server"
+                      placeholder="@username:server"
                       name="userIdInput"
                       variant="Background"
                       disabled={inviting}