* feat: [AA-950] Productize Streak Discount
- Change STREAK_DISCOUNT_EXPERIMENT_FLAG to STREAK_DISCOUNT_FLAG
- Remove references to "experiment" and ticket AA-759
- Made flag names more consistent
- Move segment event from get_bucket to streak calculation
- Streak discount event edx.bi.course.streak_discount_enabled is sent when celebrations are calculated
- Convert LegacyWaffleFlags to WaffleFlags
Co-authored-by: cdeery <cdeery@edx.edu>