Key design pointers:

• Assume the configmap name at namespace level to be "tekton-pruner-namespace-spec" (NOTE: This configmap will take priority if the enforced config level at tektonconfig/ default configmap in pipelines namespace is "namespace")
  Sample configmap: 

// code placeholder

apiVersion: v1
kind: ConfigMap
metadata:
  name: tekton-pruner-namespace-spec
  namespace: tekton-pipelines
data:
  ns-config: |
    historyLimit: 100
    successHistoryLimit: 50
    failedHistoryLimit: 100
    ttlSecondsAfterFinished: 600s