[CMS] Change the link input field into a more complex feature

**Is your feature request related to a problem? Please describe.**
If the organization ever changes domains or the slug of a page is changed, all the links referenced in pages will have to be changed manually. The effort can be quite large when dealing even with a few pages.

**Describe the solution you'd like**
A user could benefit from the selector in the `Edit menu` screen (`/admin/menus`) or the exact same selector.

**Additional context**
The selector mentioned earlier: