Adding corev1.Events to GCP PubSub channel for easier debugging

[nachocano]

Contributes to fix #724

Proposed Changes

• Adding corev1.Events to GCP PubSub channel in order to make debugging easier.
• Adding verbs to create/update/patch events to the gcppubsub default configuration
• Here is the list of the events emitted:

Channel Controller

Name	Type	Description
ChannelReadStatusFailed	Warning	When there was an error trying to get the internal status of the channel. Includes the go error string.
SubscriptionSyncFailed	Warning	When the Channel's subscription couldn't be synced. Includes the go error string.
SubscriptionDeleteFailed	Warning	When the old Channel's subscriptions couldn't be deleted. Includes the go error string.
GcpCredentialsReadFailed	Warning	When the GCP credentials couldn't be generated. Includes the go error string.
GcpResourcesPlanFailed	Warning	When there was an error creating a plan of reconciliation for the GCP resources. Includes the go error string.
GcpResourcesPersistFailed	Warning	When there was an error trying to persist the planned resources. Includes the go error string.
TopicCreateFailed	Warning	When there was an error reconciling the topic for the channel. Includes the go error string.
TopicDeleteFailed	Warning	When there was an error deleting the old topic for the channel. Includes the go error string.
K8sServiceCreateFailed	Warning	When the K8s Service couldn't be created. Includes the go error string.
VirtualServiceCreateFailed	Warning	When the Virtual Service couldn't be created. Includes the go error string.
ChannelUpdateStatusFailed	Warning	When the Channel's status couldn't be updated. It can happen even if the reconciliation process was successful. Includes the go error string.
ChannelReconciled	Normal	When the Channel's reconciliation process succeeds. This is the "Success" event. Includes the channel name.

ClusterChannelProvisioner Controller

Name	Type	Description
CcpReconcileFailed	Warning	When there was a problem reconciling the CCP. Includes the go error string.
CcpUpdateStatusFailed	Warning	When the CCP's status couldn't be updated. It can happen even if the reconciliation process was successful. Includes the go error string.
CcpReconciled	Normal	When the CCP's reconciliation process succeeds. This is the "Success" event. Includes the CCP name.

Dispatcher Controller

Name	Type	Description
DispatcherReconcileFailed	Warning	When there was a problem reconciling the dispatcher. Includes the go error string.
DispatcherUpdateStatusFailed	Warning	When the channel's dispatcher status couldn't be updated. It can happen even if the reconciliation process was successful. Includes the go error string.
DispatcherReconciled	Normal	When the dispatcher reconciliation process succeeds. This is the "Success" event. Includes the channel name.

Release Note

GCP PubSub channel has detailed information when errors occur.

[nachocano]

/cc @Harwayne

[knative-metrics-robot]

The following is the coverage report on pkg/.
Say /test pull-knative-eventing-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
contrib/gcppubsub/pkg/controller/channel/reconcile.go	97.3%	96.5%	-0.8
contrib/gcppubsub/pkg/controller/clusterchannelprovisioner/reconcile.go	96.9%	94.4%	-2.4

[Harwayne]

/lgtm

[grantr]

/approve

[knative-prow-robot]

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