config.yaml

#@ load("@ytt:data", "data")
#@ load("@ytt:yaml", "yaml")

---
kind: ConfigMap
metadata:
  name: controller-config
data:
  config.yaml: #@ yaml.encode(data.values.controller.feature_gates)

values-schema.yaml

#@data/values-schema
---
controller:
  #@schema/default []
  feature_gates:
    #@schema/validation one_of=["A", "B"]
    - ""

values.yaml

#@data/values
---
controller:
  feature_gates: []