In Product Email Campaigns Self-Managed

What does this MR do?

1. This enables in product marketing emails for self-managed instances.

   In product email campaigns are sent on 4 different topics (tracks) at various intervals, until the task for a particular track has been completed. If you're curious how the feature looks like, you can watch: https://www.youtube.com/watch?v=XEfACC5omBI

2. The CRON job that runs daily at 9 am to send out the emails is now also executed on self managed

3. The worker sends an email to all users of root groups which are in a state of onboarding specific for a track and interval who are able to perform a track's action and have opted into marketing emails.

4. We use the email_opted_in field on User alongside with the ApplicationSettings.in_product_marketing_emails_enabled to determine if a user should receive the in-product marketing email. We now automatically set email_opted_in to true if a user signs up on an instance where ApplicationSettings.in_product_marketing_emails_enabled is set.

Screenshots

Different states of the welcome screen:

• Self managed has no "sign up for company", but we show them a checkbox to opt in for emails
• .com has a "sign up for company"
  • if users sign up for company, we opt them in to emails automatically
  • if users sign up for themselves, we show them a checkbox to opt in for emails

On Self managed CE/EE	On .com setting up "just for me"	On .com setting up for company

Related to:

• Issue: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/308
• Epic: gitlab-org/growth&62