Stepper: Deprecate useSteps and create initialize

[escapemanuele]

Details

Let's add a new method to Stepper framework API called initialize . This method is an asynchronous method that is called once per flow to boot the flow. It should do any prep actions (fetch experiments, assert conditions, redirect to other flows, etc...), and most importantly return the steps.

This also deprecated the useSteps hook because it has a few flaws.

Checklist

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Related

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[escapemanuele]

Closed with #97999