feat(nginx): split nginx from dashboard

Dashboard now get's deployed seperatly from the nginx-reverse-proxy. The service nginx has been created in aura-web to act as the reverse-proxy, taking over all functionality from aura-web 1 to 1.

Fixes #111 (closed)

In addition the following tasks should be done:

• double check the documentation of this area
• allow custom locations (and nginx-config)
• allow (or document) usage of different reverse proxy (by disabling the port forwards)
• discuss whether #85 (closed) is the appropriate issue for this task
• add NGINX_VERSION to the sample-env file

Regarding NGINX_VERSION: We currently depend on using the alpine-version of nginx, since we need to install certbot manually. This installation is +/- ugly at the moment and should be refactored to only be done when required. We also might be able to implement some smart checking on which package-manager is installed - though I'd generally prefer only supporting alpine here, since it should be enough and is a decent, lightweight option.