Add Watchtower to keep the images uptodate

[aeimer]

User Story

As a:

hoster

I want:

to keep all the images uptodate

so that:

we are always running the latest version

Acceptance criteria:

• []

Additional info:

Have a look at https://github.com/v2tec/watchtower

You may only want to webhook to gitter and disable the updating for the geli related container...

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