Docker image use of public dockerhub

[mh11]

Is your feature request related to a problem? Please describe.
The e.g. Docker plain starter relies on public alpine:latest from dockerhub and a build can fail, if the pull rate limit has been reached.

Describe the solution you'd like
For internal projects point the starter to an internal container registry (or get a dockerhub licence for the company).

Describe alternatives you've considered
It would be the user's responsibility to store a copy of alpine in a registry without rate limits, which is not ideal (keeping things up-to-date, multiple copies, ...)