Provide docker container with Zephyr SDK and tooling pre-installed
Right now proper use of the pipeline requires careful setup, with scheduled pipeline and a non-default configuration for the cache. It would be much easier and faster if Zephyr SDK was pre-installed into the image. Over time other parts of the experience could be pre-installed but starting with the SDK is the right way IMO.
We may need to support multiple versions of the SDK at the same time.