The Tekton event handler is too broad

[oiricaud]

Expand and modified the default event listeners to only trigger a new pipeline run upon a merge of a PR.

Currently the event listener will trigger a webhook on a pipeline run on a push or pr-related activity

[hollisc]

Enhancement: The Tekton Trigger resources provided by Kabanero out of the box is very broad (ie. a webhook will be triggered upon every push or activity related to pull requests such as creation, modification, merge, review).

Tweak the Kabanero provided yamls so a webhook is only triggered upon the merging of a PR into a target branch.