This pulls in https://github.com/telepresenceio/watchable/ to use to communicate between components. I added a watching.md doc describing the design a bit and how to use it; I'd usually put a lot more info in the PR description, but just go read it in the markdown file. I moved the Kubernetes provider to publish its results via watchable.

As a bonus, datawire@4c1f521 is mostly moving the IR translator types over as well... but I didn't include it in this PR because something about it is causing controller-gen to crash, and I didn't want to break make generate in this PR. What's sort of weird about it is that it still writes all of the files correctly, but then crashes.

$ make generate
make --warn-undefined-variables -f tools/make/common.mk generate
make[1]: Entering directory '/home/lukeshu/src/github.com/envoyproxy/gateway'
tools/bin/controller-gen object paths="./..."
panic: interface conversion: ast.Expr is *ast.CompositeLit, not *ast.Ident

goroutine 1463 [running]:
sigs.k8s.io/controller-tools/pkg/loader.(*referenceCollector).Visit(0xc008e31a00, {0xd5da58?, 0xc00761d9c8})
        /home/lukeshu/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/loader/refs.go:136 +0xff
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