All of the code for the service mirror controller lives in the `linkerd/linkerd2/controller/cmd` package. It is typical for control plane components to only have a `main.go` entrypoint in the cmd package. This can sometimes make it hard to find the service mirror code since I wouldn't expect it to be in the cmd package.
We move the majority of the code to a dedicated controller package, leaving only main.go in the cmd package. This is purely organizational; no behavior change is expected.
Signed-off-by: Alex Leong <alex@buoyant.io>