logan-terraform: use "-raw" CLI option for terraform output
terraform output in 0.14 and above will format the output from teraform output
as HCL by default. One needs to add "-raw" to the command line
to get the unmodified value.
This technically breaks compatibility with 0.13 but since the only (automated) consumer of this wrapper is GitLab and that has moved to 0.14, it's safe to move the wrapper forward.
Closes https://gitlab.developers.cam.ac.uk/uis/devops/devhub/gitlab-deploy/-/issues/328