This creates a base library that enables us to leverage the dependency
graph to convey injection dependencies. Our controllers will start
to get their informers off of a `context.Context` via `fooinformers.Get(ctx)`.
By simply linking `fooinformers` to access the informer in this way, we trigger
a cascade of `init`-time registrations for the informer, and its transitive
dependencies (e.g. shared informer factory, client).
The `ctx` is infused with these informers in `package main` by linking the
appropriate reconcilers (transitively registering everything) and then calling
`sharedmain.Main()` (from `github.com/knative/pkg/injection/sharedmain`).
Markus Thömmes
Matt Moore