Just like Jira issues, Wiki pages can have files attached to them.
Attaching a file to a page is as simple clicking the upload button and selecting the files you want to upload, or dragging a file from your desktop into the designated upload area on the page attachments screen.
You will see a collapsed progress area that shows while files are being uploaded. Once done, the progress area disappears again
You cannot drag and drop and entire folder, but you can select multiple files to upload simultaneously.