## Description
- This PR adds a new fat-migration.yml file which will run all cases in fat container instead of dev.app.appsmith
- This PR will not affect any existing Push/Workflow dispatches as its a separate action file
- Moving to fat container will not be put into action until RBAC is live - so as to not trigger any new challenge at last minute
## Type of change
- New .yml file
## How Has This Been Tested?
- Cypress CI runs
## Checklist:
### QA activity:
- [X] Test plan has been approved by relevant developers
- [X] Test plan has been peer reviewed by QA
- [X] Cypress test cases have been added and approved by either SDET or manual QA
- [X] Organized project review call with relevant stakeholders after Round 1/2 of QA
- [X] Added Test Plan Approved label after reveiwing all Cypress test
