Change identities id column to a bigint (#9371)

Change identities id column to a bigint (#9371)

* fix: change Identity's id column to a bigint

This appears to be the last model created using a 5.0 migration,
where column types defaulted to `integer` rather than `bigint`.

This migration changes the column type to match that of all of the
other ID columns.

* Change user_id column in identities to bigint and fix down-migration