Add possibility to control spawn interval rate

[EPuncker]

Explanation of what you want to do that is currently impossible

This would be cool to set up events for faster spawn just like cip does

Desired functionality

• Being able to define spawnIntervalRate in config.lua file
• Lua script command to change it on the fly, something like Game.setSpawnRate(value[,MonsterClass])
• MonsterClass is optional and would change the spawn rate only of monsters of that class, assuming PR [Feature] Bestiary #4356 gets merged
• Default behavior would be changing all existing spawns rate
• Accept only positive values and set a cap of 24 hours max value as of this is the default max value we use for spawn file

Discussion

I don't know what format to use for value, perhaps percentage since we doesn't support float values in config to have something like 1.5 rate, feel free to make your suggestions