Wire a regular uk plug to the input terminals of the LED driver. Wire the output of the driver to the Fibaro RGBW controller. Wire your 8 garden spots in 4 pairs to the RGBW controller (it can switch 4 individual circuits via the RGBW channels) or just daisy chain all 8 lights to a single channel.
Better still, choose RGBW spots instead of white to get a full range of colours, though you’ll loose out on brightness.
The Fibaro RGBW micro can handle 6A per channel with max 12A across all 4 channels. Your 8nr 5W spots at 12v will total 3.36A
The module will also give you dimming control if chosen lamps are dimmable (didn’t check)… so not just on/off
Edit: changed driver specification for one with DC output and non-dimmable (cheaper). The dimming is done after the driver not before.
You’ll need an outside box whatever method you choose (Fibaro+Driver Or Outlet+Driver).
Bonus of the Fibaro is the small size… so your box doesent need to protrude from the wall too far. To use a Zwave outlet you’ll need a very deep box as you’ll need to allow for the depth of both the socket and the plug.