Is your feature request related to a problem? Please describe.
I cannot iterate over commits that are missing a scope.

According to the Tera docs of group-by, items that lack an attribute are discarded.

This means that if I want to have a scoped changelog, as per the git-cliff example, (and I do) then these commits are skipped from the changelog.

Describe the solution you'd like
I would like git-cliff to mark these commits in a specially named scope (maybe called unscoped? maybe have it configurable?) so I can iterate over them in my template and create a special section/heading for them

Describe alternatives you've considered
If git-cliff does not somehow mark these missing scopes, I do not believe there is an alternative on iterating over them.

Additional context
Some capture of the output of git-clif when scopes are missing:

# Changelog
All notable changes to this project will be documented in this file.

## [unreleased]

### Documentation

### Infrastructure

#### Ide

- Added git commit hooks for conventional messages
- Added suggested VS Code extensions

<!-- generated by git-cliff -->

Note the Documentation section that does not display any commits there (since the commit message is like docs: some commit message