Part of T318457.

1. ALTERs to run: DROP INDEX gemm_mentor ON /*_*/growthexperiments_mentor_mentee; ALTER TABLE /*_*/growthexperiments_mentor_mentee ADD gemm_mentee_is_active TINYINT(1) DEFAULT 1 NOT NULL; CREATE INDEX gemm_mentor ON /*_*/growthexperiments_mentor_mentee ( gemm_mentor_id, gemm_mentee_is_active );, see patch
2. Where to run those changes: growthexperiments.dblist, per-wiki x1 databases
3. When to run those changes: At any time
4. If the schema change is backwards compatible: Yes.
5. If the schema change has been tested already on some of the test/beta wikis: Schema change is deployed at beta wikis, but the accompanying feature is in-development (see parent task).
6. if the data should be made available on the labs replicas and/or dumps: The table only contains public data. It is included in dumps, and the new column should be included there as well.