Add STC8-DFN 8 with EP1.7x2.4mm

kicad-footprints!3628 (merged)

kicad-symbols!4489

I added the thermal vias variant as well, though I don't really know if it's needed. Its just a MCU after all.

https://stcmicro.com/datasheet/STC8G-en.pdf#page=81