Add documentation on scaling to 0 with KEDA

[kate-goldenring]

We have KEDA docs for autoscaling but we should tailor some docs to scale to 0 with KEDA: https://www.spinkube.dev/docs/topics/autoscaling/scaling-with-keda/

[bacongobbler]

@kate-goldenring is there supporting material out there that I can reference when updating this guide? Or would a Slack huddle to collect your thoughts on this topic be best?

[kate-goldenring]

@bacongobbler I am happy to huddle. I think appropriate steps would be the following:

1. Set up a cluster with SpinKube and KEDA as the tutorial above shows
2. Create a SpinApp with enableAutoscaling: true like this one
3. Create a KEDA ScaledObject that will scale the SpinApp deployment to 0 replicas. This KEDA tutorial seems like a good start. Particularly around setting minReplicas to 0. We'd need to decide what the trigger is.
4. Test if that works?

[kate-goldenring]

This KEDA HTTP trigger may be the best fit