refactor: standardize unauthorized access error messages in users conroller

[AdeMi20]

To ensure consistent API behavior, the differing authorization error messages in the UsersController were centralized by introducing a new UNAUTHORIZED_ACTION_MESSAGE constant at the top of the src/users/users.controller.ts file. This constant, set to 'You are not authorized to perform this action', replaced the previous hardcoded, inconsistent strings across various handler methods (such as exportData and downloadExport), thereby standardizing the authorization-related ForbiddenException errors thrown throughout the controller.

Close #697

[drips-wave]

@AdeMi20 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits