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)

tests/app/main/views/test_platform_admin.py

@@ -37,6 +37,7 @@ def test_should_redirect_if_not_logged_in(
 
 @pytest.mark.parametrize('endpoint', [
     'main.platform_admin',
+    'main.platform_admin_splash_page',
     'main.live_services',
     'main.trial_services',
 ])
@@ -589,6 +590,20 @@ def test_get_tech_failure_status_box_data_removes_percentage_data():
     assert 'percentage' not in tech_failure_data
 
 
+def test_platform_admin_splash_doesnt_talk_to_api(
+    client_request,
+    platform_admin_user,
+):
+
+    client_request.login(platform_admin_user)
+
+    page = client_request.get('main.platform_admin_splash_page')
+
+    assert page.select_one('main .govuk-body a')['href'] == url_for(
+        'main.platform_admin',
+    )
+
+
 def test_platform_admin_with_start_and_end_dates_provided(mocker, platform_admin_client):
     start_date = '2018-01-01'
     end_date = '2018-06-01'

tests/app/main/views/test_two_factor.py

@@ -1,3 +1,4 @@
+import pytest
 from bs4 import BeautifulSoup
 from flask import url_for
 from freezegun import freeze_time
@@ -107,6 +108,9 @@ def test_should_login_user_and_not_redirect_to_external_url(
     assert response.location == url_for('main.show_accounts_or_dashboard', _external=True)
 
 
+@pytest.mark.parametrize('platform_admin', (
+    True, False,
+))
 @freeze_time('2020-01-27T12:00:00')
 def test_should_login_user_and_redirect_to_show_accounts(
     client,
@@ -115,12 +119,14 @@ def test_should_login_user_and_redirect_to_show_accounts(
     mock_get_user_by_email,
     mock_check_verify_code,
     mock_create_event,
+    platform_admin,
 ):
     with client.session_transaction() as session:
         session['user_details'] = {
             'id': api_user_active['id'],
             'email': api_user_active['email_address']}
     api_user_active['email_access_validated_at'] = '2020-01-23T11:35:21.726132Z'
+    api_user_active['platform_admin'] = platform_admin
 
     response = client.post(url_for('main.two_factor'),
                            data={'sms_code': '12345'})