lgtm.com: add configuration file for building on lgtm.com

lgtm.com has some interesting scripts that try to automatically
build an autotools project and detect dependencies.

It currently doesn't work, because gobject-introspection is detected,
but pgobject is not installed. That causes a configure failure

  configure: error: "--enable-introspection aims to build the settings documentation. This requires GObject introspection for python (pygobject)

I guess we could make the configure script smarter, to ignore
introspection by default if pygobject is not workable.

On the other hand, let's simply help the project to build NetworkManager by
adding a .lgtm.yml configuration.

.lgtm.yml

@@ -0,0 +1,57 @@
+# Configuration for https://lgtm.com
+
+extraction:
+  cpp:
+     prepare:
+        packages:
+          - autoconf
+          - automake
+          - autopoint
+          - clang
+          - dbus
+          - dbus-x11
+          - dnsmasq
+          - git
+          - gobject-introspection
+          - gtk-doc-tools
+          - intltool
+          - iproute2
+          - iptables
+          - libaudit-dev
+          - libcurl4-gnutls-dev
+          - libdbus-1-dev
+          - libgirepository1.0-dev
+          - libglib2.0-dev
+          - libglib2.0-doc
+          - libgnutls28-dev
+          - libiw-dev
+          - libjansson-dev
+          - libjansson4
+          - libmm-glib-dev
+          - libndp-dev
+          - libnewt-dev
+          - libnss3-dev
+          - libpolkit-gobject-1-dev
+          - libreadline-dev
+          - libsystemd-dev
+          - libteam-dev
+          - libtool
+          - libudev-dev
+          - locales
+          - make
+          - meson
+          - mobile-broadband-provider-info
+          - pkg-config
+          - ppp
+          - ppp-dev
+          - python-dbus
+          - python-gi
+          - python-setuptools
+          - python3-dbus
+          - python3-gi
+          - python3-pip
+          - python3-setuptools
+          - udev
+     configure:
+        command:
+        - ./autogen.sh