[TektonConfig] Allows user to set priorityClassName parameter for

the tekton resources created.

In TektonConfig CR, allows  `.spec.config.priorityClassName` as a
new optional field where users can set the priorityClassName.

However, extenally the necessary Kubernetes PriorityClass needs to
be created accordingly to allow successful pod scheduling, else the
pod will not come into Running stage

docs/TektonConfig.md

@@ -35,6 +35,7 @@ The TektonConfig CR provides the following features
     config:
       nodeSelector: <>
       tolerations: []
+      priorityClassName: system-cluster-critical
     pipeline:
       disable-affinity-assistant: false
       disable-creds-init: false
@@ -86,6 +87,7 @@ Config provides fields to configure deployments created by the Operator.
 This provides following fields:
 - [`nodeSelector`][node-selector]
 - [`tolerations`][tolerations]
+- [`priorityClassName`][priorityClassName]
 
 User can pass the required fields and this would be passed to all Operator components which will get added in all
 deployments created by Operator.
@@ -100,11 +102,13 @@ config:
     operator: "Equal"
     value: "value1"
     effect: "NoSchedule"
+  priorityClassName: system-node-critical
 ```
 
 This is an `Optional` section.
 
-
+**NOTE**: If `spec.config.priorityClassName` is used, then the required [`priorityClass`][priorityClass] is 
+expected to be created by the user to get the Tekton resources pods in running state
 ### Pipeline
 Pipeline section allows user to customize the Tekton pipeline features. This allow user to customize the values in configmaps.
 
@@ -203,3 +207,6 @@ This is an `Optional` section.
 [node-selector]:https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#nodeselector
 [tolerations]:https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/
 [schedule]:https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/#cron-schedule-syntax
+[priorityClassName]: https://kubernetes.io/docs/concepts/scheduling-eviction/pod-priority-preemption/#pod-priority
+[priorityClass]: https://kubernetes.io/docs/concepts/scheduling-eviction/pod-priority-preemption/#priorityclass
+

pkg/apis/operator/v1alpha1/tektonconfig_types.go

@@ -125,4 +125,7 @@ type TektonConfigList struct {
 type Config struct {
 	NodeSelector map[string]string   `json:"nodeSelector,omitempty"`
 	Tolerations  []corev1.Toleration `json:"tolerations,omitempty"`
+	// PriorityClassName holds the priority class to be set to pod template
+	// +optional
+	PriorityClassName string `json:"priorityClassName,omitempty"`
 }

pkg/reconciler/common/transformers.go

@@ -580,6 +580,7 @@ func AddConfiguration(config v1alpha1.Config) mf.Transformer {
 
 		d.Spec.Template.Spec.NodeSelector = config.NodeSelector
 		d.Spec.Template.Spec.Tolerations = config.Tolerations
+		d.Spec.Template.Spec.PriorityClassName = config.PriorityClassName
 
 		unstrObj, err := runtime.DefaultUnstructuredConverter.ToUnstructured(d)
 		if err != nil {

pkg/reconciler/common/transformers_test.go

@@ -501,6 +501,7 @@ func TestAddConfiguration(t *testing.T) {
 				Effect:   "noSchedule",
 			},
 		},
+		PriorityClassName: string("system-cluster-critical"),
 	}
 
 	manifest, err = manifest.Transform(AddConfiguration(config))
@@ -509,7 +510,7 @@ func TestAddConfiguration(t *testing.T) {
 	d := &v1beta1.Deployment{}
 	err = runtime.DefaultUnstructuredConverter.FromUnstructured(manifest.Resources()[0].Object, d)
 	assertNoEror(t, err)
-
 	assert.Equal(t, d.Spec.Template.Spec.NodeSelector["foo"], config.NodeSelector["foo"])
 	assert.Equal(t, d.Spec.Template.Spec.Tolerations[0].Key, config.Tolerations[0].Key)
+	assert.Equal(t, d.Spec.Template.Spec.PriorityClassName, config.PriorityClassName)
 }