feat: change docker base image from ubuntu 20.04 to 22.04

This PR:

• Downgrade the ubuntu base image from 22.04. to 20.04.
• Add documentation which describes the release process
• Add documentation which describes how to build RLS locally using the same Dockerfile as the CI does (shell script also added)
• Remove .devcontainer/Dockerfile but create a symlink to utils/Dockerfile instead