Reduce usage of the platform admin index page

This page is slow to load which means:
- it’s annoying for us
- it’s potentially causing load on the database

This commit does two things to reduce the amount we’re unnecessarily
looking at this page:

1. Avoid redirecting to it when signing in as a platform admin user
2. Don’t go directly to it when clicking ‘platform admin’ at the top,
   but instead show a holding page (there’s a fair chance you’ve clicked
   that link in order to go and manage some email branding or find a
   user, not wait for stats to load)

app/main/views/platform_admin.py

@@ -42,6 +42,14 @@ ZERO_FAILURE_THRESHOLD = 0
 
 @main.route("/platform-admin")
 @user_is_platform_admin
+def platform_admin_splash_page():
+    return render_template(
+        'views/platform-admin/splash-page.html',
+    )
+
+
+@main.route("/platform-admin/summary")
+@user_is_platform_admin
 def platform_admin():
     form = DateFilterForm(request.args, meta={'csrf': False})
     api_args = {}

app/main/views/two_factor.py

@@ -111,7 +111,5 @@ def redirect_when_logged_in(platform_admin):
     next_url = request.args.get('next')
     if next_url and _is_safe_redirect_url(next_url):
         return redirect(next_url)
-    if platform_admin:
-        return redirect(url_for('main.platform_admin'))
 
     return redirect(url_for('main.show_accounts_or_dashboard'))

app/navigation.py

@@ -101,6 +101,7 @@ class HeaderNavigation(Navigation):
             'platform_admin_list_complaints',
             'platform_admin_reports',
             'platform_admin_returned_letters',
+            'platform_admin_splash_page',
             'suspend_service',
             'trial_services',
             'update_email_branding',
@@ -580,6 +581,7 @@ class MainNavigation(Navigation):
         'platform_admin_list_complaints',
         'platform_admin_reports',
         'platform_admin_returned_letters',
+        'platform_admin_splash_page',
         'pricing',
         'privacy',
         'public_agreement',
@@ -828,6 +830,7 @@ class CaseworkNavigation(Navigation):
         'platform_admin_reports',
         'platform_admin_returned_letters',
         'platform_admin',
+        'platform_admin_splash_page',
         'pricing',
         'privacy',
         'public_agreement',
@@ -1117,6 +1120,7 @@ class OrgNavigation(Navigation):
         'platform_admin_list_complaints',
         'platform_admin_reports',
         'platform_admin_returned_letters',
+        'platform_admin_splash_page',
         'pricing',
         'privacy',
         'public_agreement',

app/templates/admin_template.html

@@ -55,7 +55,7 @@
           "active": header_navigation.is_selected('user-profile')
         },
         {
-          "href": url_for('main.platform_admin'),
+          "href": url_for('main.platform_admin_splash_page'),
           "text": "Platform admin",
           "active": header_navigation.is_selected('platform-admin')
         },

app/templates/views/platform-admin/splash-page.html

@@ -0,0 +1,17 @@
+{% extends "views/platform-admin/_base_template.html" %}
+
+{% block per_page_title %}
+  Summary
+{% endblock %}
+
+{% block platform_admin_content %}
+
+  <h1 class="heading-large">
+    Summary
+  </h1>
+
+  <p class="govuk-body">
+    <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('main.platform_admin') }}">Load summary</a>
+  </p>
+
+{% endblock %}