Hello, Simon. I also park and charge my Leaf outside (not in a garage).
In the USA, the 2018 Nissan Leaf comes with an EVSE (charger cord) which is made to plug into a high-capacity electrical outlet, able to charge the Leaf at 6.6 kilowatts. The EVSE also comes with an adapter which lets the owner plug the cable into a normal American 120 volt home outlet. When using the adapter, the Leaf charges at only 1.44 kilowatts, which we call "trickle charging."
I would guess that in France, the Nissan EVSE comes with a grounded French E-type plug (230 volts, 16 amps). This would charge your Leaf at 3.68 kw, more than twice as fast as what we call "trickle charging." 3.68 kw is fast enough to add about 160 km of driving range, if the Leaf is plugged-in while you sleep each night (for 8 hours).
Because the standard American electrical outlet only provides 40% as much energy as a standard French outlet, many American Leaf owners install a high-capacity electrical outlet at their house, to allow the Nissan EVSE to charge at 5.76 kw or 6.6 kw. We call this "Level-2 charging." Your 3.68 kw E-type outlet is already "Level-2", and is probably fast enough to satisfy your charging needs.
Before you have an electrical outlet added outside for charging, I would recommend that you visit your Nissan dealer, and obtain a photograph of the electrical plug on the charging cable which will come with your Leaf. If you show that photo to the electrician, then the correct outlet can be installed.