add Pipelines Controller Observational Dashboard

The goal is to get a better understanding of how our components behave
under load so that we can make appropriate tunings/adjustments.

The following metrics are being queried for the dashboard:-

    * tekton_pipelines_controller_running_pipelineruns_count -
    Number of pipelineruns executing currently
    * tekton_pipelines_controller_running_taskruns_count -
    Number of taskruns executing currentl
    * tekton_pipelines_controller_taskruns_pod_latency
    Scheduling latency for the taskruns pods
    * tekton_pipelines_controller_workqueue_depth -
    The workqueue for the Tekton Pipelines controller
    * Pipelines controller restarts
    * tekton_pipelines_controller_client_resutls -
    Total number of K8s API requests made by Pipelines Client

Signed-off-by: Satyam Bhardwaj <[email protected]>