chore: Add opacity token

Author: AhmedAmineZr

app/lib/ui/tokens/opacity/opacity_screen.dart

@@ -75,6 +75,7 @@ class OpacityScreen extends StatelessWidget {
   List<OpacityTokenItem> _getOpacityTokenItems(OudsThemeContract currentTheme) {
     return [
       OpacityTokenItem(name: 'invisible', value: currentTheme.opacityTokens.invisible),
+      OpacityTokenItem(name: 'weakest', value: currentTheme.opacityTokens.weakest),
       OpacityTokenItem(name: 'weaker', value: currentTheme.opacityTokens.weaker),
       OpacityTokenItem(name: 'weak', value: currentTheme.opacityTokens.weak),
       OpacityTokenItem(name: 'medium', value: currentTheme.opacityTokens.medium),