feat: make tekton optional

[ElderMatt]

📌 Summary

This PR makes tekton an optional app.

Newly created cluster will have tekton disabled by default.
Upgraded clusters will have a migration where the enabled property is added to tekton and set to true.

Tekton pipelines also has a added priorityClass so that tekton pipeline managed pods have a lower priority.

[svcAPLBot]

Comparison of Helm chart templating output:

@@ data.VERSIONS @@
! ± value change in multiline text (one insert, one deletion)
  
- {"api":"main","aplCharts":"main","console":"main","consoleLogin":"main","core":"main","specVersion":57,"tasks":"main","tools":"main"}
+ {"api":"main","aplCharts":"main","console":"main","consoleLogin":"main","core":"main","specVersion":58,"tasks":"main","tools":"main"}




@@ spec.resourcetemplates.0.spec.taskRunTemplate.podTemplate @@
# triggers.tekton.dev/v1alpha1/TriggerTemplate/trigger-template-demo-ext-repo-buildpacks-public-trigger
! + one map entry added:
+ priorityClassName: tekton-low


@@ spec.resourcetemplates.0.spec.taskRunTemplate.podTemplate @@
# triggers.tekton.dev/v1alpha1/TriggerTemplate/trigger-template-demo-ext-repo-private-trigger
! + one map entry added:
+ priorityClassName: tekton-low

@@ spec.resourcetemplates.0.spec.taskRunTemplate.podTemplate @@
# triggers.tekton.dev/v1alpha1/TriggerTemplate/trigger-template-demo-ext-repo-public-trigger
! + one map entry added:
+ priorityClassName: tekton-low

@@ spec.resourcetemplates.0.spec.taskRunTemplate.podTemplate @@
# triggers.tekton.dev/v1alpha1/TriggerTemplate/trigger-template-demo-java3-v0-0-1
! + one map entry added:
+ priorityClassName: tekton-low


@@ data @@
! + one map entry added:
+ default-pod-template: |
+   priorityClassName: tekton-low


@@ apps.tekton @@
! + one map entry added:
+ enabled: true

@@ versions.specVersion @@
! ± value change
- 57
+ 58

[CasLubbers]

Tested on fresh cluster and works ✅