Add lastNobilityAdvanceAt field and update logic in FalukantService

- Introduced a new field `lastNobilityAdvanceAt` in the FalukantUser model to track the last time a user advanced in nobility.
- Updated the `FalukantService` to enforce a one-week cooldown between nobility advancements, throwing an error if the user attempts to advance too soon.
- Ensured the `lastNobilityAdvanceAt` field is updated with the current date upon a successful nobility advancement.

backend/models/falukant/data/user.js

@@ -44,6 +44,10 @@ FalukantUser.init({
             key: 'id',
             schema: 'falukant_data'
         }
+    },
+    lastNobilityAdvanceAt: {
+        type: DataTypes.DATE,
+        allowNull: true
     }
 }, {
     sequelize,