Push button momentary switch, unknown model. Had it around. Button was too wide and needed to be filed on two sides to make it narrow.

There are two very narrow walls in the project that can be gone after slicing - these are not really needed for this enclosure to be sturdy.

Button connected to raspberry pi 3 GPIO 3 (pin 5) and GND (pin 14 or other for GND).

GPIO 4 (pin 7) connected to logic level mosfet N-channel (via 390Ω resistor; for gpio output protection) gate (G) pin. That pin also pull-down to GND via 10kΩ resistor (so led light is default off and internal mosfet capacity is discharged). Drain (D) mosftet pin connected to negative of led strip. Source (S) mosftet pin connected to prusa power supply GND. Raspberry pi GND and prusa power supply GND are connected, too.

leds powered from internal supply of the prusa printer.

Encolsure OctoPrint plugin properly configured to control both GPIO pins. 

Light can now be turned on via button at printer, using OctoPrint web panel or using OctoPod mobile app.