Use predefined name for cache bucket
Derive the cache bucket name from a predefined variable instead of relying on a random UUID.
Expand variables in the gitlab-runner values.yaml
file before running
helm. This allows us to further parameterize the runner config which is
by default not broken out very well in the gitlab-runner chart.
Increment the terraform state to start from scratch. The cluster must be torn down and created from scratch after this change is merged.