feat: conditional subject-empty

### Expected Behavior

It would be great to have conditional **subject-empty** (not just `always` or `never`).

Because some `types` might not always require a subject:

```sh
# Here, subjects are required to understand the context (ie. what happened in the fix or feature)
fix(foo): bar
feat(foo): bar

# Here, subjects could be optionals as the scope is enough to understand the context (ie. no need to explain what I changed in the README)
docs(README)
chore(deps)
refactor(foo)
style(bar)
```

### Current Behavior

**subject-empty** is either `always` or `never`, not conditional.

### Affected packages

- [ ] cli
- [X] core
- [ ] prompt
- [ ] config-angular

### Possible Solution

_No response_

### Context

_No response_