fix: ensure all default Sass spacing scale config can be overwritten (ex. lang-specific spacing options like we have with Japanese)

Author: sghoweri

packages/core/styles/01-settings/settings-spacing/_settings-spacing.scss

@@ -9,13 +9,13 @@
 
 // Unit on which all spacing is based
 /// Bolt gutter spacing value
-$bolt-spacing-gutter: 2rem;
+$bolt-spacing-gutter: 2rem !default;
 /// Bolt default leading spacing value
 $bolt-spacing-leading: 1.65 !default;
 /// Bolt squished spacing value
-$bolt-spacing-squished: 0.5;
+$bolt-spacing-squished: 0.5 !default;
 /// Bolt stretched spacing value
-$bolt-spacing-stretched: 1.5;
+$bolt-spacing-stretched: 1.5 !default;
 
 /// Bolt's definition of spacing scale. Used within 'export-data()' to JSON.
 /// @type Map
@@ -28,7 +28,7 @@ $bolt-spacing-values: (
   'large': 2,
   'xlarge': 4,
   'xxlarge': 8,
-);
+) !default;
 
 @include bolt-export-data('spacing/scale.bolt.json', $bolt-spacing-values);