Add ease score onboarding in product marketing email

What does this MR do?

This adds an experience track email to the in product marketing emails. It includes a short survey where the user is asked to rate the ease of onboarding.

Part of issue: gitlab-org/growth/engineering#5437 (closed)

Design: https://litmus.com/builder/b25715c

Depends on: !60832 (merged) and !61146 (merged)

Screenshots

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