fix: Move content into to frontend directory

Doing this BEFORE the merge prevents a lot of merge conflicts.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/src/components/common/countdown-button/countdown-button.tsx

@@ -0,0 +1,33 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import React, { useState } from 'react'
+import type { ButtonProps } from 'react-bootstrap'
+import { Button } from 'react-bootstrap'
+import { useInterval } from 'react-use'
+
+export interface CountdownButtonProps extends ButtonProps {
+  countdownStartSeconds: number
+}
+
+/**
+ * Button that starts a countdown on render and is only clickable after the countdown has finished.
+ *
+ * @param countdownStartSeconds The initial amount of seconds for the countdown.
+ * @param children The children that should be displayed after the countdown has elapsed.
+ * @param props Additional props given to the {@link Button}.
+ */
+export const CountdownButton: React.FC<CountdownButtonProps> = ({ countdownStartSeconds, children, ...props }) => {
+  const [secondsRemaining, setSecondsRemaining] = useState(countdownStartSeconds)
+
+  useInterval(() => setSecondsRemaining((previous) => previous - 1), secondsRemaining <= 0 ? null : 1000)
+
+  return (
+    <Button disabled={secondsRemaining > 0} {...props}>
+      {secondsRemaining > 0 ? secondsRemaining : children}
+    </Button>
+  )
+}