Refactor onStartCommand method to use switch statement for action handling

[Epic-R-R]

Refactor onStartCommand method in OblivionVpnService for improved action handling.

This refactor replaces multiple if-else statements with a switch statement, enhancing readability and maintainability by centralizing Intent action dispatching for starting and stopping the VPN service (FLAG_VPN_START and FLAG_VPN_STOP).

Key Changes:

• Simplified action handling logic using a switch statement.
• Ensured compatibility with existing functionality.
• Thoroughly tested for correct behavior with various Intent actions.

[markpash]

Thanks for the PR ❤️