PodSpec has this as a slice, and if we wanted to start creating these references more automatically for e.g. Deployment it isn't immediately obvious which secret is used for which image (certainly without reading the secrets). This changes it to a more pass-through model for simplicity.
Fixes: https://github.com/knative/caching/issues/9
* Add the initial caching type definitions.
This is largely carried over from https://github.com/knative/serving/pull/1972
* Incorporate feedback from @evankanderson
* Add the CRD for the type definition.
This adds all of the elements needed to bootstrap the knative/caching repo.
I've tried to limit this to largely boilerplate elements so that it can more easily be recycled as we create other repos.
Matt Moore