Add Roundcube Webmail Installation Support

[nguyentranchung]

We plan to integrate Roundcube Webmail into FlashPanel, allowing users to install and manage a web-based email client easily.

Key Features:
• One-click installation of Roundcube on the mail server.
• Automatic configuration with the existing mail server setup.
• Secure authentication and seamless integration with existing email accounts.
• Option to enable/disable webmail access via the FlashPanel UI.

Use Case:
Users can access their email accounts through a user-friendly webmail interface without needing third-party mail clients.