Refactor loop registry

[cedric-cordenier]

As I was doing some exploration of the loop registry, I found the code to be hard to modify and quick tightly coupled together. This is my attempt to clean some of this up.

In particular, I:

• Collapsed the command factory into the loop registry: these were invariably getting called one after another so this seemed a no-brainer
• Separated the handling of GRPCOpts from the registration of the loop itself.

This also makes it easier to add a handle to the loop into the registry at a later date if desirable.

@krehermann Please push back if there's something I'm missing

[github-actions]

I see that you haven't updated any README files. Would it make sense to do so?

[krehermann]

looks better. thanks for cleaning it up

[cl-sonarqube-production]

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[github-actions]

This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days.