Add packaging label to changelog generator config

[wren]

More work with #1112

We added dependabot and told it to use a new packaging label. This
change gives that label its own separate section in the changelog.

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have tested this code locally.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.
• All tests pass.

[micahellison]

📦📄