Allow setting min_master_version

Given the work on https://gitlab.developers.cam.ac.uk/uis/devops/raven/infrastructure/-/issues/153 it seems that it will be necessary to be able to set the min_master_version variable on the google_cluster_compute resource in this module. I also require it for the upcoming raven-core migration due to an issue deploying Autopilot GKE clusters > 1.23.