Augment CD with Feature Flags

Let's enhance the CD pipeline with not only GitOps but also [Feature Flags](https://www.martinfowler.com/articles/feature-toggles.html). This will enable more custom control over the SDLC stages such that two stages that use equivalent environments can share an environment rather than redeploy.

Feature Flags enable engineering to separate code deployment from feature rollout. For example, a team can use [LaunchDarkly](https://launchdarkly.com/features/feature-flags/) to deploy new features to production but hide them so that no one can use them, then make them available in stages to additional groups until everyone has access. This can replace or augment a separate staging environment and be used to perform A/B testing, canary testing, and blue/green deployment. Stages in the SDLC don't necessarily have to be separate deployment environments (namespaces, clusters, etc.), but in some cases can be code deployed in the same environment that is exposed for use by different stages.