[ci] Investigate Cue and Dhall

Created by: ggilmore

cue and dhall are two solutions that can help us address the following problems:

• We have four separate configuration deployment targets: Docker-Compose, Pure-Docker, Kubernetes, and sourcegraph-server. Keeping configuration changes between all of them can be challenging
• Reduce boiler plate and duplication (from our perspective)
• Cue and Dhall can validate the raw configuration files including any edits made by external tools (e.g. bash scripts)
• Cue and dhall can be driven by outside tools (e.g. our CI pipeline) and can open up the possibility of fully automated deployments for sourcegraph.com and k8s.sgdev.org.
• (optional) our customers can use them to manage their customizations to our deployment