[5.x] Add submitting state for confirmation modal to better visualise a running action

[morhi]

I noticed that when confirming an action that is running for a few seconds it is hard to determine if something is actually happening. This made me submitting the form twice and actually trigger an error, because the action could not be run a second time.

This PR adds a nice (hopefully nice enough) loader to visualise that there is an action running in the background.

https://github.com/user-attachments/assets/96f94595-f635-459d-a5b1-04f6d9f75f4c

Also fixes in issue with the "Create Folder" action, which submitted the form twice when pressing enter on the submit button.