[1.0.2] Fix error in skip links for the main navigation menu

The wrapper div has been deleted (by mistake?) in 🐛 [beta4] Accessibility issues in header modals (id/aria-labelledby, button title) Fixed .
let's re-introduce this wrapper and the issue will be solved.

3 solutions:

• let's reintroduce the wrapper in the same position as before, inside the header component, but it must be a prop and we need a random default value, in order to avoid duplication of HTML ID, and inject from page.html.twig:
  

    {{ pattern('header', {
     ...
    skip_id: "header-navigation"
    }) }}

• let's put a similar wrapper around the header in page.html.twig:
  

  <div id="header-navigation">
    {{ pattern('header', {
     ...
    }) }}
  </div>

• let's leverage the attribute object:
  

    {{ pattern('header', {
       ....
      attributes: {
        id: "header-navigation"
      }
    }) }}

the third solution with "let's leverage the attribute object:", is not ok,
because the skip links are pointing to the header and not to the menu..

i have proposed something.
should work fine, please review

Why did you do rename mobile_menu_id to menu_id ?

Also, you pushed this unexpected change on nav_menu:

-            {% set item_id = menu_id ~ "-" ~ loop.index %}
+            {% set item_id = menu_id ~ '-' ~ loop.index %}

the mobile part of the menu_id was removed indeed, the menu is the same for mobile and not for mobile.

the twig-cs-fixer program added the simple quote in nav_menu :)