Show total disk size of each backup run

[makemrproper]

As a user I want to know how large the daily backups I am doing are taking up on my drive.
It is practical for me if the web interface can inform me of this.

Such as in the summary under BACKUPS -> LISTINGS

[jdaviescoates]

I believe this is coming in 9.0

Edit: actually I think perhaps I'm wrong about that https://forum.cloudron.io/post/99869