contractnumber provider added, old provider number field only if no previous contact exist

backend/prisma/migrations/20260208132553_add_previous_provider_fields/migration.sql

@@ -0,0 +1,7 @@
+-- AlterTable
+ALTER TABLE `Contract` ADD COLUMN `previousContractNumber` VARCHAR(191) NULL,
+    ADD COLUMN `previousCustomerNumber` VARCHAR(191) NULL,
+    ADD COLUMN `previousProviderId` INTEGER NULL;
+
+-- AddForeignKey
+ALTER TABLE `Contract` ADD CONSTRAINT `Contract_previousProviderId_fkey` FOREIGN KEY (`previousProviderId`) REFERENCES `Provider`(`id`) ON DELETE SET NULL ON UPDATE CASCADE;