Update all packages in pubspec.yaml

[dJani97]

Describe the use-cases of your feature

Oftentimes when I open an older project, almost ALL my dependencies have newer versions. While this package helps tremendously in updating them, it's still a tedious process to click on them one-by-one, hit Alt-Enter, and hit "Update package".

Describe your solution

When more than one update is available, it would be nice to have an "Update all packages" option.