Variations of this get asked all the time, and the fact is that it's very difficult to quantify factors such as friction. If you use basic physics to determine the torque required you will get an extremely low number, that will not work in practice.
You can either build the drum mechanism first and then measure it. Or, the more practical approach which is to basically guess if you had a lever of a certain length attached to it, how many kg would you have to apply to the lever to turn the drum?
An example of a reasonable guess might be 2kg at the end of a 30cm lever. That's 20 newtons * .3m = 6nm torque.
It's better to buy a motor that's slightly too strong, rather than one that's too weak that has to be replaced, so lets double that estimate to 12nm torque.
Keep in mind that "powerful" is not what you need. Power is rated in watts, and more power allows you accelerate the drum faster and reach higher top speeds. You likely don't care about this. What you care about is the ability to turn the drum at all, and that's a matter of torque.
Case and point, a very tiny motor the size of your thumb with a large gear reduction will be able to turn this, it will just turn slowly. A huge motor the size of your fist with no gearbox might struggle.