Add documentation and examples for eventing.v1 components.

[vaikas]

What is changing? (Please include as many details as possible.)

Adding eventing.v1 resources. This means Broker, Trigger, EventType

How will this impact our users?

They can use v1 API shape.

In what release will this take happen (to the best of your knowledge)?

v0.16

Context

Link to associated PRs or issues from other repos here.

1. Eventing v1 api eventing#3372

Additional info

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