feat: Upgrade bootstrap to 5.3.0 and enable dark mode

Fixes ietf-tools#3365

Author: larseggert

ietf/static/css/ietf.scss

@@ -15,7 +15,7 @@ $popover-max-width: 100%;
 $font-family-sans-serif: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", "Noto Sans", "Liberation Sans", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
 $font-family-monospace: "Noto Sans Mono", SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
 
-// Enable automatic dark mode
+// Allow color modes
 
 $color-mode-type: media-query;