Add download size and estimated time when downloading upgrades
The progress bar text should provide an idea of how much work has been completed, in MB.
An estimate of the time left until the operation is complete should also be included in the progress bar text. Indicate that the “time left” is an estimate using the word “about”.
An alternative would be to display only the elapsed time.
Implementation-wise, zenity does not allow any of the above, so this can only happen after #6461 is resolved.