LIMS-2206: Assume DHL when no courier specified

[ndg63276]

JIRA ticket: LIMS-2206

Summary:

When the shipping service is used, it doesn't specify a courier when sending data back to ispyb. If Synchweb is trying to track a shipment, and the courier is blank, we should assume DHL. There is a check for the correct number of digits anyway.

Changes:

• Assume DHL if courier is blank or null

To test:

• This has been deployed to ispyb-dev-3, complete with DHL credentials
• Go to a recently shipped DHL dewar eg /shipments/sid/80525
• Check tracking is working, eg

• Set the courier blank and repeat the check, ie

update Shipping set deliveryAgent_agentName="" where shippingId=80525;

• Set the courier to NULL and repeat the check, ie

update Shipping set deliveryAgent_agentName=NULL where shippingId=80525;