Add an "alignx" option to the images.Text to control whether the value of the "x" option is the left border of the text (current behaviour), the center of each line or the right border.
Fixes#10849
To sort an image's colors from darkest to lightest, you can then do:
```handlebars
{{ {{ $colorsByLuminance := sort $image.Colors "Luminance" }}
```
This uses the formula defined here: https://www.w3.org/TR/WCAG21/#dfn-relative-luminanceFixes#10450
