Add an outlet to this switch?
This is a 3-way switch being used in 1-way mode.  Note that nothing is attached to the second traveler (brass) screw.  That's a perfectly fine setup.  With only a single cable to the switch, it is not a &quot;power to the switch first&quot; setup.
There is only one cable going into this light.   That means it's not a &quot;power to the light first&quot; setup either.
Yes, that means it's something you're unfamiliar with.
There's clearly some sort of third junction.  I'm getting the impression you think the switch is inconvenient for where the light is.  Maybe our third junction is at a light which is appropriately located for that switch, and either you don't know about it (burned out before you moved in?) or it has been removed but the box left.  Or, the box is somewhere else entirely, or in the service panel.
Regardless, all this to say, you can have the light and switch, or you can have the GFCI, but you can't have both...
And separate from all that, you can't alter the premises without permission from the landlord...
And separate from all that, you can't do electrical work on a rental unit (even if you own it) unless you are a licensed electrician.