Add Settings window to Agent UI

Agent systray UI has been extended with
a setting window that allows configuring 
management URL, admin URL and 
supports pre-shared key.
While for the Netbird managed version 
the Settings are not necessary, it helps
to properly configure the self-hosted version.

client/ui/netbird.desktop

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Name=Netbird Agent
+Exec=/usr/bin/wiretrustee-ui
+Icon=netbird
+Type=Application
+Terminal=false
+Categories=Utility;
+Keywords=netbird;