Using plugins needing config with Kong 2.0.0 is broken

[jfrancisco0]

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Summary

Updating from Kong 1.5.0 to 2.0.0 causes many error messages relating to plugin configuration, resulting in a non-functional Kong.

Kong Ingress controller version
0.7.0

Kong or Kong Enterprise version
Kong 2.0.0

Kubernetes version

Client Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.2", GitCommit:"59603c6e503c87169aea6106f57b9f242f64df89", GitTreeState:"clean", BuildDate:"2020-01-23T14:21:54Z", GoVersion:"go1.13.6", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"14+", GitVersion:"v1.14.9-eks-c0eccc", GitCommit:"c0eccca51d7500bb03b2f163dd8d534ffeb2f7a2", GitTreeState:"clean", BuildDate:"2019-12-22T23:14:11Z", GoVersion:"go1.12.12", Compiler:"gc", Platform:"linux/amd64"}

Environment

• Cloud provider or hardware configuration:
  Amazon EKS

What happened

Using Kong 2.0.0 with plugins needing configuration (KongPlugin with config: field), we get the following errors:

controller.go:119] unexpected failure updating Kong configuration:
posting new config to /config: 400 Bad Request {"fields":{"plugins":[{"run_on":"unknown field"}]},"name":"invalid declarative configuration","code":14,"message":"declarative config is invalid: {plugins={{run_on=\"unknown field\"}}}"}
W0129 17:25:24.899531       1 queue.go:112] requeuing kube-system/prometheus-operator-kubelet, err posting new config to /config: 400 Bad Request {"fields":{"plugins":[{"run_on":"unknown field"}]},"name":"invalid declarative configuration","code":14,"message":"declarative config is invalid: {plugins={{run_on=\"unknown field\"}}}"}

Expected behavior

Plugin (and Kong) should operate normally

Steps To Reproduce

1. Set up Kong 1.5.0 with ingress controller 0.7.0
2. Configure a Kong plugin that needs configuration (e.g. request-transformer)
3. Update Kong to 2.0.0