Refactor - The worker should drop privileges after allowing itself access to the Docker daemon

Description

!115 (merged) introduced support for communicating with the Docker daemon over the standard UNIX socket instead of a TCP socket. This, however, requires the worker to have r/w access to the socket, which is not possible with the worker running as AuTA. Right now it runs as root, but this is not desirable.

Priority

Medium - As far as we know, there are no RCE vulnerabilities in the worker, but at least some extra degree of protection would be very nice.

Definition of done

When the worker does not have to run as root to access the socket or if the worker can grant its own user access and then drop privileges