==== Background
To facilitate works on mentor dashboard, we need to move mentor/mentee relationship to a separate table. For more details, see {T275773}.
==== Task objective
Do the mentor/mentee relationship migration on Wikimedia wikis.
==== Checklist
[ ] Set migration stage to `SCHEMA_COMPAT_WRITE_OLD | SCHEMA_COMPAT_READ_OLD` both on beta and prod (no-op)
[ ] Set migration stage to `SCHEMA_COMPAT_WRITE_BOTH | SCHEMA_COMPAT_READ_OLD` on beta and make sure relationship is written to both places
[ ] Run `mwscript extensions/GrowthExperiments/maintenance/migrateMentorMenteeRelationship.php` on all beta wikis with GE installed
[ ] Set migration stage to `SCHEMA_COMPAT_WRITE_BOTH | SCHEMA_COMPAT_READ_NEW` on beta and watch for breakages
[ ] Wait for {T278573} to be completed
[X] Wait for the [maintenance script](https://gerrit.wikimedia.org/r/c/mediawiki/extensions/GrowthExperiments/+/675192) to get merged
[ ] Set migration stage to `SCHEMA_COMPAT_WRITE_BOTH | SCHEMA_COMPAT_READ_OLD` on production and make sure mentor/mentee relationship data is written to database
[ ] Run `mwscript extensions/GrowthExperiments/maintenance/migrateMentorMenteeRelationship.php` on all wikis in growthexperiments.dblist in production
[ ] Set migration stage to `SCHEMA_COMPAT_WRITE_BOTH | SCHEMA_COMPAT_READ_NEW` on production
[ ] Wait a week to ensure there are no breakages
[ ] Set migration stage to `SCHEMA_COMPAT_WRITE_NEW | SCHEMA_COMPAT_READ_NEW` both in beta and production (**this is the point of no return**)