Convert SearchFields to GovukSearchFields

Changes those fields in the following forms:
- SearchByNameForm
- SearchUsersByEmailForm
- SearchUsersForm
- SearchNotificationsForm

Includes changes to templates that use this form
and associated tests.

tests/app/main/views/test_activity.py

@@ -363,7 +363,7 @@ def test_shows_message_when_no_notifications(
         {},
         {},
         'Search by recipient',
-        '',
+        None,
     ),
     (
         {
@@ -371,7 +371,7 @@ def test_shows_message_when_no_notifications(
         },
         {},
         'Search by phone number',
-        '',
+        None,
     ),
     (
         {
@@ -441,7 +441,7 @@ def test_search_recipient_form(
     assert(len(recipient_inputs) == 2)
 
     for field in recipient_inputs:
-        assert field['value'] == expected_search_box_contents
+        assert field.get("value") == expected_search_box_contents
 
 
 @pytest.mark.parametrize('message_type, expected_search_box_label', [

tests/app/main/views/test_find_services.py

@@ -69,5 +69,5 @@ def test_find_services_by_name_validates_against_empty_search_submission(
     client_request.login(platform_admin_user)
     document = client_request.post('main.find_services_by_name', _data={"search": ""}, _expected_status=200)
 
-    expected_message = "You need to enter full or partial name to search by."
-    assert document.find('span', {'class': 'error-message'}).text.strip() == expected_message
+    expected_message = "Error: You need to enter full or partial name to search by."
+    assert document.find('span', {'class': 'govuk-error-message'}).text.strip() == expected_message

tests/app/main/views/test_find_users.py

@@ -87,8 +87,8 @@ def test_find_users_by_email_validates_against_empty_search_submission(
     client_request.login(platform_admin_user)
     document = client_request.post('main.find_users_by_email', _data={"search": ""}, _expected_status=200)
 
-    expected_message = "You need to enter full or partial email address to search by."
-    assert document.find('span', {'class': 'error-message'}).text.strip() == expected_message
+    expected_message = "Error: You need to enter full or partial email address to search by."
+    assert document.find('span', {'class': 'govuk-error-message'}).text.strip() == expected_message
 
 
 def test_user_information_page_shows_information_about_user(