Generates the migration of Chime's tables in the app's repo: the one that installs them, or, after an upgrade of Chime, the one that brings them to its latest version.
$ mix chime.gen.migration
$ mix chime.gen.migration --repo MyApp.Repo
It is mix phoenix_mountable.gen.migration Chime.Migrations: the version
the app is at is read from its migrations, and the new migration pins the
latest (see Chime.Migrations). Run it with mix ecto.migrate.