Provide docs for a headless out-of-the-box docker Jenkins for tests

[krichter722]

I'm in the process of investigating a bug of Jenkins template engine and am building a SSCCE for use case. I stumbled over The 'local development' section of the docs which describes the setup of a test Jenkins which requires a lot of manual configuration and provides a UI which is of no use for the case a simple reproducer for a bug.

It'd be nice to have instructions and a ready docker container for a one liner which allows to test the local pipeline and prints the job logs from a mounted volume.