Add a script to migrate the columns (which can also
be executed in dry run), and a config option with the migration stage
(defaults to SCHEMA_COMPAT_OLD).
Some of the script-related code is stolen from
Ic755526d5f989c4a66b1d37527cda235f61cb437.
Bug: T220791
Change-Id: I7460a2d63f60c2933b36f8383a8abdbba8649e12