POC: Render the user profile tabs in Vue Router

What does this MR do and why?

Refactors the current profile_tabs.vue to a route rendered in a Vue Router. This is the ground work needed so that we can progressively move the individual tab items and move them into the sidebar menu (see #389842).

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

1. In rails console enable the profile_tabs_vue feature flag

   Feature.enable(:profile_tabs_vue)

2. Visit a user's profile page (http://localhost:3000/root)
3. There should be no functional difference. Both the sidebar menu and tabs should work normally.

Related to #389842 #497477 (closed)

lib/sidebars/user_profile/panel.rb

@@ -26,8 +26,8 @@ def super_sidebar_context_header
       private
 
       def add_legacy_menu?
-        # When `profile_tabs_vue` feature flag is enabled, legacy profile views
-        # will be replaced by components in `app/assets/javascripts/profile/components/router_views`
+        # When `profile_tabs_vue` feature flag is enabled, legacy profile pages
+        # will be replaced by routes in `app/assets/javascripts/profile/components/app.vue`
         Feature.disabled?(:profile_tabs_vue, context.current_user)
       end