Added idempotency check to migration.

Author: 5Amogh

src/main/resources/db/migration/dbiemr/V23_AMM1959_DHIS_USER.sql

@@ -1 +1 @@
-ALTER TABLE db_iemr.m_user ADD COLUMN dhistoken VARCHAR(255);
+ALTER TABLE db_iemr.m_user ADD COLUMN IF NOT EXISTS dhistoken VARCHAR(255);