Updated Mobile DevOps docs page

What does this MR do and why?

This MR adds more details and some usable examples to the Mobile DevOps docs page. The intent with this change is to give users a more detailed starting point for adopting GitLab Mobile DevOps.

Related to gitlab-org/incubation-engineering/mobile-devops/readme#115 (closed)

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How to set up and validate locally

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MR acceptance checklist

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