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If the Campaign and Assign To are valid, then create the application associated to the External Partner.
For Campaign association, we can use CampaignId and for User Assignment we can use AssigntoEmail.
If the external partner is already linked to an application, then we would need to define whether that Application gets reassigned.
If the AssigntoEmail is NULL, do not reassign.
If the AssigntoEmail is NOT NULL, then reassign the application to the new user.
If an Application is not linked to the External partner, then create a new application linked to the external partner if the AssigntoEmail and CampaignId fields are provided