Create backup UI does not inform user about the creation progress

[alinefm]

When you create a new backup, a message is displayed on top of the page saying the backup was started. From that until the backup is generated there is no feedback to user that an operation is being done. It would be better to what something similar to what Kimchi does when creating/cloning a guest. A dummy input is added to the list with a loading icon. When the operation finishes, that input is updated to the real data.