Add issue link to comment in controller yaml

In commit 49a7fa2 we added
a workaround for an issue that can cause the tekton controller
to be delayed launching taskruns for the first time.

This commit updates the comment on the workaround to include
an issue link with more information about the reason for the
workaround.

config/controller.yaml

@@ -95,7 +95,8 @@ spec:
               fieldPath: metadata.namespace
         # These phony AWS credentials are here to work around a bug in the aws go sdk
         # that causes extremely long delays in the execution of tasks after the initial
-        # deployment of the Tekton Pipelines controller.
+        # deployment of the Tekton Pipelines controller. See issue https://github.com/tektoncd/pipeline/issues/4087
+        # for more information.
         - name: AWS_ACCESS_KEY_ID
           value: foobarbaz
         - name: AWS_SECRET_ACCESS_KEY