What should the force option do

### Checklist

- [x] I added a descriptive title
- [x] I searched open requests and couldn't find a duplicate

### What is the idea?

I was under the "presumption" that `-force` would effectively remove the old directory on linux/mac and install a fresh environment.

I was wrong apparently.

Would it be desirable to change this behavior?

### Why is this needed?

I think the ability to have a "1 command clean installer" is really nice

```
bash miniforge.sh -f
```

just to wipe your old stuff.

### What should happen?

add of an `rf -rf ${PREFIX}` in the header.

### Additional Context

i somewhat use constructor to ship payload that is much larger than just `conda`