Link outputsourceBindings to build

[shashwathi]

Below is a pipeline with a task which has an input source to push-kritis and outputs the image to kritisImage resource. Currently there is no mechanism to capture the kritisImage metadata.
We need this information to use specific version of resource in further tasks of the pipeline.

apiVersion: pipeline.knative.dev/v1alpha1
kind: Pipeline
metadata:
  name: kritis-pipeline
  namespace: default
spec:
  tasks:
    - name: push-kritis              
      taskRef:
        name: build-push
      inputSourceBindings:
        - name: kritis-app-github
          key: workspace 
          resourceRef:
            name: kritis-repo-git
      outputSourceBindings:
        - name: kritisImage
          key: builtImage 
          resourceRef:
            name: kritis-resources-image

Expected Behavior

Build or TaskRun should hold resource references to outputSourceBindings generated.

Actual Behavior

outputSourceBindings of task is not used.

Additional Info

This should be completed before tackling: #148
This change might require build to be rendered inside build-pipeline.