I am trying to configure Kubernetes RBAC in the least-permissive way possible and I want to scope my roles to specific resources and subresouces. I\'ve dug through the doc
You can find the resources list of Kubernetes v1.9 from here: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.9/#-strong-api-overview-strong- . For other K8s versions, check the 'API Reference' section on https://kubernetes.io/docs/reference/
Check the catalog on the left side, for example, 'Workloads' is the high-level overview of the basic types of resources such as Container, Deployment, CronJob etc. And these subresources like 'Container, Deployment, CronJob' are the typical basic Kubernetes API resources.
You can access these basic resources via kubectl, hence there also have a list of 'Resource types' available in https://kubernetes.io/docs/reference/kubectl/cheatsheet/
But I'm confusing in your statement "a the subresource that governs a a part of a Deployment's spec--the container image", if you are trying to manage the permissions of an container image, you should do it on your image registry, but not on Kubernetes side. For example, your registry should has an access controller to do authentication when user pulling images.