include mail command in docker image

[himpierre]

Is your feature request related to a problem? Please describe.
I'd like to send the reports of a popeye scan via email. That's not possibe at the moment with the default docker image used by the suggested cronjob.

Describe the solution you'd like
Well, as I told above. :) So it would be nice to have the mail command included.

Describe alternatives you've considered
Building my own docker image / using a side car