Prompt user when a long link has been shortened before

[lisatjide]

Is your feature request related to a problem? Please describe.
It is not uncommon that the same page could be shortened by multiple shortlinks. To prevent too many shortlinks are taken up pointing to the same long link, we can remind users that a shortlink created to point to the same destination on link creation modal, the prompt will also lead user to the directory which shows the search results of shortlinks that points to that particular long link.