Migrate bot_type column to user_type
Single generalized field is used for determining user type, can be used for STI if needed. Other db columns (e.g.
ghost) can be migrated too later on.
Features with higher risk:
- Code review analytics
- Internal Bot related features
- Data migration is be required for quite big table.
- New indexes and update of old indexes are required.
- Remove old column in separate issue\MR.