As Steven says, that transformer is intended to be PCB mounted using its solder tags.
However, if you wish to mount it to the steel panel directly a very usual way is to add a "clamp" as seen below - copied from here. You could make something similar. In this case your wiring will be on one side and you would need to connect wires to it and insulate them for safety. Using a PCB arrangement will be easier in many cases.
The makers are in Carlsbad, New Mexico, USA, but people would be able to manufacture similar clamps easily in Turkey. Note the side portions which stop the transformer sliding out of the main loop. You could just make a simple square C sguare loop with feet relatively easily BUT the screws have to provided enough pressure and friction to stop the core sliding out sideways.
IF the core has mounting holes or IF it is stell and can be safely drilled, you can do something like below. If the core is ferriote it would pro=bably be destroyed by drilling. The method below and a number of others are shown here