feat: useScrollPosition 커스텀 훅 추가

Author: gitul0515

src/hooks/useScrollPosition.js

@@ -0,0 +1,5 @@
+import useSessionStorage from './useSessionStorage';
+
+const SCROLL_POSITION_KEY = 'prevPostIndex';
+
+export default () => useSessionStorage(SCROLL_POSITION_KEY, 0);