Command "#set add" to add an item to a list in settings

## Describe your suggestion
> With as much detail as possible, describe what your suggestion would do for Baritone.

New commands : `#set add`, `#set remove`, `#set clear`.

Those commands would serve to add or remove items in a list in the settings.

### Examples

```
#set remove acceptableThrowawayItems stone
```

```
#set add acceptableThrowawayItems andesite,diorite,granite
```

## Settings
> If applicable, what settings/customizability should be offered to tweak the functionality of your suggestion.

## Context
> Describe how your suggestion would improve Baritone, or the reason behind it being added.

In [USAGE.md](https://github.com/cabaletta/baritone/blob/master/USAGE.md#commands), `acceptableThrowawayItems` is listed as a setting that's "*fun / interesting / important that you might want to look at changing in normal usage of Baritone*".

However, during "normal usage of Baritone", using `#acceptableThrowawayItems dirt,cobblestone,netherrack` is a bit clunky if you want to add or modify your list.

Even in abnormal usage while editing `settings.txt`, it looks like this :

```properties
acceptableThrowawayItems Optional[ResourceKey[minecraft:item / minecraft:dirt]],Optional[ResourceKey[minecraft:item / minecraft:cobblestone]],Optional[ResourceKey[minecraft:item / minecraft:netherrack]]
```

Off-topic
I'd suggest using JSON or YAML to store settings. No, seriously, I mean it. It's so much easier for both developers and users to work with an established standard rather than trying to parse programmatically or mentally a format that no one else ever uses.

The problem is that there's no way to add/modify a list, only to override it. And copying old values has to be done manually, which is tedious if there's many, many items in that list. I think a command to add/remove items from a list in the settings would be very appropriate. This way, during normal usage of Baritone, one could add/remove an item from the list without having to copy everything.

## Final checklist
- [x] I know how to properly use check boxes
- [x] I have not used any OwO's or UwU's in this issue.