Add paste-to-upload attachment support in comment textbox

## Summary A user requests the ability to upload attachments by pasting them directly into the textbox when posting a comment in the posts/feeds area. ## Steps to Reproduce Not provided. ## Expected Behaviour Pasting an attachment (e.g., an image or file) into the comment textbox should automatically upload it as an attachment. ## Actual Behaviour Currently, pasting an attachment into the comment textbox does not trigger an upload. ## Environment Not provided. --- *Reported by **retoor** via DevPlace.*