Add user_table.creation_time to ESG Gateway user-related principal objects.

Note NCAR migrated principals date_created reflects conversion date and time. The original ESG-II user creation time should be preserved. This original creation time should be applied to the new ESG Gateway user objects.

Note: subsequent data conversions (for example the PCMDI user database) should also preserve the original user creation time.

Note this may require JDBC/direct SQL manipulation of the target database objects.