feat: added 2FA configuration and modified readme.md with required instructions

[chirag0002]

Pull Request: Add 2FA Configuration to OpenVPN Admin Portal

Description:

This pull request introduces two-factor authentication (2FA) configuration to the OpenVPN admin portal. The setup utilizes the Google Auth PAM OpenVPN plugin alongside the google-authenticator package for enhanced security.

Key Changes:

• Added 2FA configuration to OpenVPN admin portal using the Google Auth PAM OpenVPN plugin.
• Integrated the google-authenticator package for generating and validating time-based one-time passwords (TOTP).
• Configured the setup to work exclusively on a local host machine (Docker compatibility issues were addressed, and Docker was excluded from this setup).
• Ensured that the changes do not interfere with the existing OpenVPN flow, preserving the current functionality.
• Updated the README with instructions for enabling the new 2FA configuration.

Notes:

• The 2FA configuration works seamlessly when set up on a local machine.
• Docker is not compatible with this 2FA setup at this moment, and the changes were made accordingly to avoid disruptions in the existing flow.
• After enabling the mentioned configuration in the README, the setup should function perfectly.