Update work item type migration guidelines
What does this MR do and why?
Add two considerations we should have when writing a migration that adds a new work item type, widget definition or any other data migration related to work item types.
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Related to #453986 (closed)