feat: Colored grade segments extended from default 5 to default 12

  This implementation updates color scheme in grade range to 12. The fix
  ensures consistent color of grade letters accross courses.

  Note:
  Convert the default five grade letter setting entry in edx-platform/cms/envs/common.py

  From
  DEFAULT_GRADE_DESIGNATIONS = ['A', 'B', 'C', 'D']

  To
  DEFAULT_GRADE_DESIGNATIONS = ['A+', 'A', 'A-', 'B+', 'B', 'B-', 'C+', 'C', 'C-', 'D+', 'D’]

Author: haftamuk

src/grading-settings/scss/_variables.scss

@@ -4,4 +4,11 @@ $grading-scale-segment-colors: (
   2: #F6BF58,
   3: #FF7E6A,
   4: #E94949,
+  5: #4f2934,
+  6: #ce4c87,
+  7: #B30349,
+  8: #2b0312,
+  9: #f3b2c7,
+  10: #A60649,
+  11: #9f0c40a0
 );