Update pubsub to use secrets and fix serving version to v1alpha1.

[n3wscott]

No description provided.

[knative-metrics-robot]

The following is the coverage report on pkg/.
Say /test pull-googlecloudplatform-cloud-run-events-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/pubsub/v1alpha1/topic_lifecycle.go	78.3%	75.0%	-3.3
pkg/reconciler/topic/controller.go	93.3%	77.3%	-16.1
pkg/reconciler/topic/resources/names.go	Do not exist	100.0%
pkg/reconciler/topic/resources/publisher.go	71.4%	81.8%	10.4
pkg/reconciler/topic/topic.go	67.3%	53.6%	-13.7

[vaikas]

can we bring up the test coverage for the components on a followup PR...
/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: n3wscott, vaikas-google

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [n3wscott,vaikas-google]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment