Allow injection of custom policies (3scale operator)

apiVersion: apps.3scale.net/v1alpha1
kind: APIManager
metadata:
  name: example-3scale
spec:
  wildcardDomain: <wildcardDomain>
  apicast:
    productionSpec:
       customPolicies:
           - name: custom-policy1
             version: "0.1"
             secretRef: 
                name: custom-policy1-secret
           - name: custom-policy2
             version: "0.1"
             secretRef: 
                 name: custom-policy2-secret

apiVersion: v1
data:
  apicast-policy.json:   CONTENT OF THE POLICY METADATA (required)
  init.lua: CODE OF THE POLICY (required)
  example.lua: CODE OF THE POLICY (optional)
  other.lua: CODE OF THE POLICY (optional)
kind: Secret
type: Opaque