Add scan free trial user worker

relate https://jihulab.com/gitlab-cn/gitlab/-/issues/3701+

depend on

• Add free-trial user mailer (!2120 - merged)
• Block free trial user (!2122 - merged)
• Patch subscription portal client for purchase list (!2123 - merged)

What does this MR do and why?

add scan free trial user worker

• run at 0 20 * * * which is UTC time, run everyday 4 in early morning
• business scenario in #3701 description
• high level logic explanation
  • build paid_user_hash from all namespaces of paid plan + paid ci + paid storage
  • build expired_user_hash from all namespaces of expired plan + expired storage (ci doesn't expire)
  • loop all human but not forbidden user, find out free trial start date
  • do block or send free trial email logic if need