TSR: Modify Onboarding API to treat PostalCode as blank when "0" is passed

Currently when TSR UI does not have any data for Postal Code of a candidate, it send value as "0" zero to Workterra AP. In Workterra we have validation to accept either blank values fro address field or validate it against country specified. So, when Postal code is passed - WT checks for it's associated country to check the postal code format. This results in a validation error and employee record is not getting added to Workterra.

Until TSR fixes this, as a workaround we are now converting the postal code value to blank (if it is passed as zero '0' ) in Workterra while storing employee data.