The official Jenkins image can be easily extended to pass in the configuration in files. That's how it is designed to work, and it has worked quite well for me.
If you'd like to see one way to do it, look at the lts-with-plugins branch of my docker repo,
https://github.com/MarkEWaite/docker/tree/lts-with-plugins . I've also added credentials and agents and many other configuration settings by committing files to a private repository similar to that one.
I use docker images to test the Jenkins git plugin and the Jenkins git client plugin and have been very pleased with how well Jenkins works with complex setups in a docker environment.
I'm sure there are others with much better techniques than mine, but you're welcome to refer to my techniques as one way of doing it.
Mark Waite