ConsumerVPN for VPNKit 6

Please see the ConsumerVPN macOS Client Readme document to get started.

What's New:

• Added kVPNManagerConfigurationNameKey key at connectionOptions, which value will be VPN configuration name.
• Added VPNOnDemandConfiguration at VPNConfiguration to handle VPN On Demand settings.
• Added unregister notifications on view disappear.
• Added VPNAPIManager cleanup() call while application terminates.
• Rename kStayConnectedOnQuit to kVPNStayConnectedOnQuit which ensure that connections are not killed off when the app dies during an active connection.
• Rename installHelperAndConnectOnInstall() method to synchronizeConfiguration(), which responsible to updates VPN configuration.
• Replace login() API with loginWithRetry() after purchase success.
• Added installSystemExtension() API to install WireGuard System Extension.