Add trigger to a pipeline

[siamaksade]

Add an action to the pipeline context menu to be able to add a trigger a pipeline. Adding a trigger would create the required Tekton resources (EventListener, TriggerTemplate, etc) in order to configure triggers and expose a webhook url that user can add to the Git provider repository settings. Example:
https://github.com/tektoncd/triggers/tree/master/examples/github

User should be able to easily get access to the webhook url associated with the pipeline after triggers are configured.

[siamaksade]

Should this be through Tekton CLI or k8s API?