new_notes_location

### 🚀 The feature, motivation and pitch

Could new_notes_location include a directory/folder as an option?
I think a dir (inside a workspace) was an option at some point (as I'm sure it worked with my 0_Inbox) but now it doesn't..

```
-- Where to put new notes. Valid options are
-- * "current_dir" - put new notes in same directory as the current buffer.
-- * "notes_subdir" - put new notes in the default notes subdirectory.
new_notes_location = "notes_subdir",
```

### Alternatives

_No response_

### Additional context

_No response_

Trace the implementation of the new_notes_location option and compare the existing current_dir and notes_subdir behaviors, including the reported 0_Inbox workspace case. Determine how a directory option should be represented and where its behavior is documented or tested. Done means new notes can be placed in a configured directory inside the workspace without breaking the existing options.

Written by the indexing model from the issue text.