Use `file` type CI/CD Secrets with `K8S_SECRET_ XXX` variables

https://docs.gitlab.com/ee/ci/variables/#file-type

Am curious if there's any plans to support K8S_SECRET_ prefixed CI/CD vars with the "file type"? The documentation doesn't seem specific, either way. When I try it with my repos, like K8S_SECRET_XXX with a bunch of ipsum lorem paragraphs in it, I get inside a running deployment container the environment set, but to a nonexistent build file. eg: XXX=/builds/x/ci.tmp/K8S_SECRET_XXX

I'm keenly interested in this because we've got ~37 GitLab repos deployed to two kubernetes clusters (and over 170 deployments when factoring in review apps) and a file-as-secret would be very helpful.

(tangent drift: the other Thing is would love if could specify volumes and volumeMounts YAML stanzas in the relatively new .gitlab/auto-deploy-values.yaml repo file somewhere to inject into the main GitLab CI/CD auto-deploy-app -- because then I wouldn't have to maintain a custom chart! 8-)

Proposal

Add a new variable type K8S_FILE_SECRET_ and update the secrets helper to include them.