578842 Fix Addon Name Incosistency in Addon Assignment Version

What does this MR do and why?

The migration updates all the numeric values in addon assignment versions to their proper string equivalents

See the other fix for CH here !210100 (merged)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Check the records and update them to numeric values if you don't have any

$ bundle exec rails console

$ GitlabSubscriptions::UserAddOnAssignmentVersion.all

• Run bin/rails db:migrate

• Check again to see the records updated in subscription_user_add_on_assignment_versions

MR acceptance checklist

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 #578842