Expose a button in the Network panel to open nm-connection-editor

[Amr Ibrahim]

Upstream reverted showing the desktop launcher of nm-connection-editor because it's confusing for the average user, its icon is outdated and does not follow the current GNOME icon design guidelines.
https://gitlab.gnome.org/GNOME/network-manager-applet/issues/55
https://gitlab.gnome.org/GNOME/network-manager-applet/commit/a0c31ed5

Upstream follow-up bug: Remove runtime dependency on network-manager-applet (nm-connection-editor)
https://gitlab.gnome.org/GNOME/gnome-control-center/issues/512

So in the meantime I suggest exposing a button in the Network panel (or else where it fits) to open nm-connection-editor in order not to lose the tool's functionally. The name of the button could be Advanced Network Configuration.

Note: we are already doing the same thing for Region & Language settings and Printer settings.