How to make a circuit to pulse an output when a momentary switch is released
You can do this using a 555 in a monostable configuration and, as you said, a pushbutton switch and an extra capacitor and resistor to trigger the pulse. See the attached image.

R2 is a pullup resistor to keep the trigger high. The pushbutton switch will normally be connecting the capacitor to the trigger pin which will also keep the capacitor charged through R2. When the button is pressed the capacitor will be shorted to ground and simultaneously disconnected from the trigger pin, so the trigger pin will still be pulled up by R2. However, when the button is released, it will connect the now discharged capacitor to the trigger pin which will pull it below 1/3 Vdd momentarily, before it is recharged through R2. Per the datasheet, pulling the trigger pin below 1/3 Vdd will trigger the pulse set by R1 and C2, in this case to give you a ~30ms pulse.