Clean-up Zephyr docker
Current Zephyr Docker (v3.2.0) has some workaround tricks to allow application building, which is not very convenient for actual use. (The CI docker scripts makes copies and link of host repository, which implies a possible loss of host folder in case of misuse).
Rework the Docker image and use he "--gf" option of west update
(using a group) to prevent s2opc fetches.
Edited by Jérémie Chabod