feat: add support for sub routes under /my-account (#6218)

* feat: add support for sub routes under /my-account

closes #6217

* feat(plugins/client-routes): page titles

Add support for adding custom page titles in client routes.

* fix(client/PluginPages): reload component upon URL change

* Styling

* docs(plugins): update registerClientRoute

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Co-authored-by: Chocobozzz <me@florianbigard.com>

support/doc/plugins/guide.md

@@ -872,6 +872,11 @@ To create a client page, register a new client route:
 function register ({ registerClientRoute }) {
   registerClientRoute({
     route: 'my-super/route',
+    title: 'Page title for this route',
+    parentRoute: '/my-account', // Optional. The full path will be /my-account/p/my-super/route.
+    menuItem: { // Optional. This will add a menu item to this route. Only supported when parentRoute is '/my-account'.
+      label: 'Sub route',
+    },
     onMount: ({ rootEl }) => {
       rootEl.innerHTML = 'hello'
     }