Change EventType of CloudBuildSource

[bharattkukreja]

Fixes #1608

Proposed Changes

• Change CE type of CloudBuildSource from com.google.cloud.build.event to google.cloud.cloudbuild.build.v1.statusChanged
• Update CloudBuildSource data schema

Release Note

BREAKING CHANGES

- CloudBuildSource type is updated to match event types in googleapis/google-cloudevents

ACTION REQUIRED

- Users who depend on the CloudBuildSource "type" value in the trigger filters can create new triggers with new filter value (see details below)

DETAILED CHANGES

1. CloudBuildSource event type was updated to be compliant with https://github.com/googleapis/google-cloudevents/tree/master/proto/google/events/cloud. CloudBuildSource data schema was updated to be https://github.com/googleapis/google-cloudevents/blob/master/proto/google/events/cloud/scheduler/v1/data.proto 
2. Type changes:
   CloudBuildSource: was "com.google.cloud.build.event" => now "google.cloud.cloudbuild.build.v1.statusChanged"

[bharattkukreja]

cc @nachocano

[nachocano]

/approve
/lgtm

/hold for @capri-xiyue to look at

[knative-test-reporter-robot]

The following jobs failed:

Test name	Triggers	Retries
pull-google-knative-gcp-wi-tests	2020-08-25 22:58:25.461 +0000 UTC	1/3

Automatically retrying due to test flakiness...
/test pull-google-knative-gcp-wi-tests

[capri-xiyue]

@bharattkukreja Can you also help update the docs of cloud build source with the updated event type and schema https://github.com/google/knative-gcp/blob/master/docs/examples/cloudbuildsource/README.md ?

[bharattkukreja]

@capri-xiyue Seems like googleapis/google-cloudevents#57 got merged. I have corrected the schema.

[capri-xiyue]

/lgtm

[capri-xiyue]

/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bharattkukreja, capri-xiyue, nachocano

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[capri-xiyue]

/unhold