Add missing log options to documentation

[malud]

Couper has several log options but some of them are missing at https://docs.couper.io/ . The source files for the documentation are located here.

The DOCKER.md contains options which are not documented.
At least the parent log field and maybe other.

So the task is to differ the docs markdown with the docker options and add the missing parts to the docs markdown file.

The documentation website can be run locally from /docs/website with npm ci && npm run dev