Evaluate the Tekton pull request reporting

[ccojocar]

Evaluate the Tekton pull request reporting: https://github.com/tektoncd/pipeline/blob/master/docs/resources.md#pull-request-resource

[ccojocar]

Reporting command which is built into the Tekton pipeline for GitHub:
tektoncd/pipeline#895
tektoncd/pipeline#778

[jstrachan]

for now we're going with our own webhook handler to trigger meta pipeline + handle ChatOps

we can revisit in the future. We're hoping to use Tekton for reporting pipeline status to git

[ccojocar]

@wbrefvem I am going to take over and evaluate the Tekton Pull Request resource (https://github.com/tektoncd/pipeline/blob/master/docs/resources.md#pull-request-resource).