feat: Introduce admin user management API with user listing, retrieval, account activation/deactivation, and case-insensitive role validation.

Backend/src/validators/usermanagement.validator.ts

@@ -0,0 +1,9 @@
+import Joi from "joi";
+
+export const getUserByIdValidator = Joi.object({
+    id: Joi.number().required().messages({
+        'number.base': 'ID must be a number',
+        'number.empty': 'ID is required',
+        'number.required': 'ID is required'
+    })
+})