Cactus modification

[Themostrandom]

• [ x ] This PR has been tested locally
• This mod for Minetest adds damage when players come into contact with cactus, making the game more realistic by simulating the damage caused by thorny plants.
• Suggestion : https://discord.com/channels/447819017391046687/448136308108296213/1274930814588686457

[LoneWolfHT]

This uses ABMs, which should be an absolute last measure.
It also uses get_objects_inside_radius(), but only operates on players.

This would be much better as a globalstep, looping through minetest.get_connected_players() and checking their position.

I personally prefer making the cactus do node damage like fire, and reducing its collisionbox and/or selectionbox (I forget which one has to be changed) by 0.1 or so, which IIRC makes it damage you if you touch it, the last time I did a mod like that was 0.4.x though