Provide created_date for our system users as that is mandatory

Currently the migration fails with:

    Caused by: org.h2.jdbc.JdbcSQLException: NULL not allowed for column "CREATED_DATE"; SQL statement:
    INSERT INTO PUBLIC.T_USER (id, login, password, first_name, last_name, email, activated, lang_key, created_by) VALUES ('1', 'system', '$2a$10$mE.qmcV0mFU5NcKh73TZx.z4ueI/.bDWbj0T1BYyqP481kGGarKLG', NULL, 'System', NULL, TRUE, 'en', 'system') [23502-182]