Gas smell in kitchen

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There shouldn't be any problem to ask the landlord to check what's going on. Who fixes what depends on who is the landlord, and how much rent is paid, and other factors. It may or may not be spelled out in a contract, but for sure, you can ask the landlord to check, and he can take the ball at that point, or not.
Regarding the soap solution, it needs very little liquid soap to little water to check for leaks when the solution bubbles. If you have 2 adjustable wrenches, you could tighten the connection yourself. You may or may not need some teflon tape, depending on whether tightening the connection corrected the leak or not. Those are the typical leak problems. More rarely, cracked or damaged hoses or clamps that aren't tight enough will cause leaking gas.

The guy that delivers your gas can fix those problems, as well as a plumber. They are very cheap to fix, taking less than a minute of time and maybe a very small amount of teflon tape (10 pesos for a whole roll of it ). A hose that leaks because cracked, can have the cracked part cut off, and the rest of the hose will probably be fine, and then, re-clamp it to the gas fitting.