Third Party Resources (TPR) have been removed from Kubernetes for
roughly 2 years. This commit removes the support dex had for them.
Documentation has been updated to reflect this and to instruct users
on how to migrate from TPR-powered dex environment to a Custom Resource
Defintion (CRD) based one that dex > v2.17 will support
ghodss/yaml converts from YAML to JSON before attempting to unmarshal.
This allows us to:
* Get the correct behavor when decoding base64'd []byte slices.
* Use *json.RawMessage.
* Not have to support extravagant YAML features.
* Let our structs use `json:` tags
