Add ar_id and el_id sequences for PostgreSQL

PostgreSQL needs sequences created before nextval
is used as the default value, populating newly
created fields.

Followup to: Ib6b0fc3736d173fa4ba7b786ecfc710b2f4711bb

Bug: 56185
Change-Id: Ia21d5bddead257a33a13e3ff2ec508041843613b
(cherry picked from commit a52b64ea714ca239034ec06c35d15c016121b226)