Add migration about station maintainers
Add migration about station maintainers

This migration was apparently accidentally omitted in df653b5dcf.

aptiko/enhydris,kickapoo/enhydris,aptiko/enhydris,aptiko/enhydris,openmeteo/enhydris,kickapoo/enhydris,ellak-monades-aristeias/enhydris,ellak-monades-aristeias/enhydris,ellak-monades-aristeias/enhydris,openmeteo/enhydris,kickapoo/enhydris,openmeteo/enhydris