Miscellaneous improvements for the next release

[alexashley]

• [x] split single file into config and enforcer packages
  • [x] config
  • [x] enforcer
• [x] extract Helm chart and add it to rode/charts
  • [x] update RBAC to allow for reading secrets
• [x] add unit tests
• [x] allow for passing a flag to enable/disable TLS verification when talking to registries
• [x] populate the review result so that we get more information in this response: Error from server: admission webhook "k8s-enforcer.rode.io" denied the request without explanation
• [x] handle DockerHub images
  • [x] remove the default registry from the url
  • [x] remove library from repo name
  • [x] read from imagePullSecrets for registries that require authentication
  • [x] update the README
  • [x] local development
  • [x] project background and how to run/deploy