As an Admin, I want to configure the missing issues threshold per instance during DC to Cloud migration

Currently, Xray can ignore up to 100 missing issues during migration. If there are up to 100, the migration succeeds; if there are more, the migration fails. 

It might be beneficial to make this threshold configurable per instance. This would allow each team to define an acceptable limit for missing issues based on their project size and migration tolerance, rather than relying on a global fixed value.

This flexibility would help larger instances avoid unnecessary migration failures while still ensuring that smaller projects maintain strict data integrity standards.