Merge branch 'override-bootstrap4-font-hierarchy' into 'master'

Override default font family hierarchy of bootstrap 4

Closes #47493

See merge request gitlab-org/gitlab-ce!19542

app/assets/stylesheets/framework/variables.scss

@@ -814,3 +814,5 @@ $secondary: $gray-light;
 $input-disabled-bg: $gray-light;
 $input-border-color: $theme-gray-200;
 $input-color: $gl-text-color;
+$font-family-sans-serif: $regular_font;
+$font-family-monospace: $monospace_font;