Move Build onto the injection-gen based controller infrastructure.

[mattmoor]

I've broken this into finer grained commits as a sort guide for migration. I can try to take a crack at doing something along these lines for tekton as well, but the goal of the broader refactoring was to effectively eliminate boilerplate outside of pkg/reconciler/foo for writing controllers, and keep our various controllers from drifting apart as we add features (e.g. this gives Build various metrics integrations including stackdriver that I believe it lacked previously).

This also enables us to pretty trivially consolidate controllers, or split them apart by simply changing what goes into the main binary.

/hold

cc @bobcatfish @vdemeester @n3wscott

[vdemeester]

@mattmoor nice ! I'll look into that for tekton :angel:

[knative-metrics-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/build/build.go	69.8%	65.6%	-4.2
pkg/reconciler/build/controller.go	Do not exist	100.0%

[mattmoor]

@vdemeester let me or @n3wscott know if you run into any trouble :)

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ImJasonH, mattmoor

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/knative/build/blob/master/OWNERS)~~ [ImJasonH,mattmoor] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[mattmoor]

/hold cancel