Add admin config to auto delete messages

[lil5]

It would be nice if the admin could auto delete messages after a certain time 1month,3months,1year,5years

[balzack]

I agree with this feature request. It's in my backlog as other people have asked for it as well.

Is it desirable to auto-delete messages even if space is not needed? I am just wondering if the delete after X years should only invoked if some storage threshold is met.