Create Docker container for running CI checks

[stephanosio]

Create a Docker container for running the CI check scripts that do not require the toolchains (e.g. compliance, coding guideline, ...).

The purpose of this is to eliminate (or at least, reduce) the number of the external infrastructure dependencies.

After this, the Docker containers used in the Zephyr CI will be as follows:

• ci (docker-image): CI container for running twister
• ci-check (docker-ci-check, NEW): CI container for running check scripts

Related issue: #26 -- consider using the proposed ci-check image for the documentation build workflow as well.