Different bullets for different characters

### 🚀 The feature, motivation and pitch

AFAIK, there are three characters which are converted to bullets. `*`, `-` and `+`, If there is more I'm not aware.

So I'm using the example configuration for bullets mentioned in the README

```
ui = {
bullets = { char = "•", hl_group = "ObsidianBullet" },
}
```
This will use the same bullet for all those chars. _**Can we have a feature to add different bullets for different chars ?**_
So, for e.g. something like,

```
ui = {
bullets = {
["*"] = { char = "⦾" hl_group = "ObsidianBullet" },
["-"] = { char = "⦿" hl_group = "ObsidianBullet" },
....
},
}
```

**Motivation**:
We add headings with `#, ##,` etc. However, underneath a header, I also have levels. I use `*` as top level point and `-` and `+` as sublevels / subpoints for a topic. It would really be great if those had difference bullets, if possible.

### Alternatives

_No response_

### Additional context

_No response_

Start with the bullets configuration example in the README, then trace how the plugin converts `*`, `-`, and `+` into bullets. Define per-character configuration for the output character and highlight group, and verify that each supported input marker renders according to its own setting.

Written by the indexing model from the issue text.