Moved interfaces, created new folders for visa requests and handlers

SchengenVisaApi/ApplicationLayer/Applicants/IApplicantsRepository.cs

@@ -0,0 +1,7 @@
+using ApplicationLayer.Common;
+using Domains.ApplicantDomain;
+
+namespace ApplicationLayer.Applicants;
+
+/// Repository pattern for <see cref="Applicant"/>
+public interface IApplicantsRepository : IGenericRepository<Applicant> { }