Redis Provider/Agent

[markmandel]

Is your feature request related to a problem? Please describe.

If you want to have an custom orchestration with Quilkin right now, you have to write your own xDS provider endpoint - which can be a fair amount of work, and not the simplest thing to do either.

Describe the solution you'd like

We have most of the infrastructure on the Quilkin side already with Providers and Agents.

So we could use a state store that works well for mutable information - Redis would be great for this.

Traefik does this already, so I expect there is a bunch of prior art we could steal there for configuration information as well.

Describe alternatives you've considered

Let people create their own xDS implementations -but that definitely seems like a lot of work - especially as we now have our own proto types in the mix as well.

Additional context

#780 (comment)