Implement upgrade page

Author: HVossi92

lib/uptimer_web/components/layouts/app.html.heex

@@ -29,6 +29,17 @@
           <!-- User Authentication -->
           <ul class="flex items-center gap-3 sm:gap-4 text-sm">
             <%= if @current_user do %>
+              <li>
+                <.link
+                  navigate={~p"/upgrade"}
+                  class="text-gray-600 dark:text-gray-300 hover:text-blue-600 dark:hover:text-blue-400 flex items-center transition-colors"
+                >
+                  <span class="mr-1">
+                    <.icon name="hero-sparkles" class="h-4 w-4" />
+                  </span>
+                  <span class="hidden sm:inline">Upgrade</span>
+                </.link>
+              </li>
               <li class="hidden sm:flex items-center text-gray-600 dark:text-gray-300">
                 <span class="mr-2"><.icon name="hero-user-solid" class="h-4 w-4" /></span>
                 <span class="truncate max-w-[150px]">{@current_user.email}</span>