Refactor MailKitClientFactory to remove semaphore and recreate a client for each connection

[sammychinedu2ky]

Summary

The initial implementation worked well in a scoped DI setup, ensuring that each web request received a fresh SMTP client. However, in an Orleans grain scenario where grains can remain active for extended periods, the SMTP client may become disconnected due to inactivity.

Describe your changes here.

• Removed the SemaphoreSlim as it was no longer needed.
• Ensured that a new SmtpClient instance is created for each request to prevent stale connections.