Improve the Experiment rollout template

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Created from ideas in gitlab-org/growth/team-tasks#905 (comment 2751541042)

We currently don't have clear guidelines on how or what to validate.

1. We should break up the validation of:
   • user experience
   • tracking event validation
2. We should also make it clear the steps for validation staging vs production as they can differ, so they should have their own sections.
3. Create a section where the engineer provides the pretty print json dump of the tracking events for the user journey from snowplow micro for an artifact of proof.