* Introduce `NewContext`, deprecate `NewImplFull`.
Our generated `NewImpl` methods have long taken `context.Context`, but despite many iterations the forms we expose from our `controller` package never have. This change contains several elements:
1. Expose a new `NewContext` method that takes `context.Context` in addition to the current `NewImplFull` signature.
2. Call `NewContext` instead of the deprecated `NewImpl` from our generated controller code.
3. Call `NewContext` from all our webhook reconcilers.
* Add a Tracker to controller.Impl to cut down on downstream boilerplate.
By combining our validation logic into our mutating webhook we were previously allowing for mutating webhooks evaluated after our own to modify our resources into invalid shapes. There are no guarantees around ordering of mutating webhooks (that I could find), so the only way to remedy this properly is to split apart the two into separate webhook configurations:
- `defaulting`: which runs during the mutating admission webhook phase
- `validation`: which runs during the validating admission webhook phase.
The diagram in [this post](https://kubernetes.io/blog/2019/03/21/a-guide-to-kubernetes-admission-controllers/) is very helpful in illustrating the flow of webhooks.
Fixes: https://github.com/knative/pkg/issues/847
Matt Moore
Dave Protasowski
Matt Moore