Sources v1beta1 conversions

[Harwayne]

Helps with #615.

Proposed Changes

• Adds the v1beta1 Source types to the API server.
  • CloudAuditLogsSource
  • CloudPubSubSource
  • CloudSchedulerSource
  • CloudStorageSource
• Adds a conversion webhook that converts between v1alpha1 and v1beta1.

CloudAuditLogsSource, CloudPubSubSource, CloudSchedulerSource, and CloudStorageSource now exist in both v1alpha1 and v1beta1 versions. The versions are identical. All existing objects will continue to work. All valid configurations for the objects will continue to be valid. 

If you wish, you may start using the v1beta1 API surface. If you choose not to, then everything will continue to work as-is.

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Harwayne

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[Harwayne]

/test pull-google-knative-gcp-integration-tests

[Harwayne]

/test pull-google-knative-gcp-integration-tests

[Harwayne]

/test pull-google-knative-gcp-integration-tests

[knative-metrics-robot]

The following is the coverage report on the affected files.
Say /test pull-google-knative-gcp-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/convert/conversion_helper.go	Do not exist	96.4%
pkg/apis/events/v1alpha1/cloudauditlogssource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1alpha1/cloudpubsubsource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1alpha1/cloudschedulersource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1alpha1/cloudstoragesource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1beta1/cloudauditlogssource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1beta1/cloudpubsubsource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1beta1/cloudschedulersource_conversion.go	Do not exist	100.0%
pkg/apis/events/v1beta1/cloudstoragesource_conversion.go	Do not exist	100.0%
pkg/apis/pubsub/v1alpha1/pullsubscription_conversion.go	90.9%	82.6%	-8.3
pkg/apis/pubsub/v1alpha1/topic_conversion.go	80.0%	78.3%	-1.7

[Harwayne]

This is now ready for review.

[yolocs]

/lgtm

[knative-prow-robot]

@Harwayne: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-google-knative-gcp-unit-tests	5e79a73	link	/test pull-google-knative-gcp-unit-tests

Full PR test history. Your PR dashboard.

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