Add support for `raw` variables

Summary

Add support for variables that shouldn't get expanded with the environment variables.

Support getting a raw flag from GitLab on variables. This should result in the variable being treated literally - i.e. no substitution should be performed in it.

There is already an MR implementing part of this that needs to be completed: !904 (closed)

Links

!904 (closed)

!1882 (merged)