Update work item type migration guidelines (two additional requirements)
We need to update the work item type migration guidelines to include two new requirements:
- Since we need migrations to be regular migrations, these migrations should be backwards compatible (if code in the MR that introduces the new type or widget definitions is rolled back, but migration is not, the code should still work with the new records in the DB).
- The migration time should not exceed migration timelines
MR discussion
This can be a regular migration as long the data migration doesn't exceed the [timeline guidelines](https://docs.gitlab.com/ee/development/migration_style_guide.html) and is backward compatible.
If this data migration is executed to production and staging, and then the code changes are rollbacked (note the `down` methods are not executed during rollbacks), would the application code still work correctly?
Could you please expand https://docs.gitlab.com/ee/development/work_items.html#write-a-database-migration to mention these two requirements?