Allow services to turn international SMS on/off

We didn’t make this self-service before because the pricing information
wasn’t published (ie we had to send it to services that asked for it).

Now that we publish pricing information in the app, there’s no reason
why services can’t make an informed decision about whether they want
international SMS or not.

So this commit:
- removes the platform admin button
- adds some radio buttons that our users can click with their mice

tests/app/main/views/test_service_settings.py

@@ -1176,40 +1176,59 @@ def test_switch_service_disable_letters(
     assert mocked_fn.call_args == call(service_one['id'], {"permissions": []})
 
 
+@pytest.mark.parametrize('permissions, expected_checked', [
+    (['international_sms'], 'on'),
+    ([''], 'off'),
+])
+def test_show_international_sms_as_radio_button(
+    client_request,
+    service_one,
+    mocker,
+    permissions,
+    expected_checked,
+):
+    service_one['permissions'] = permissions
+
+    checked_radios = client_request.get(
+        'main.service_set_international_sms',
+        service_id=service_one['id'],
+    ).select(
+        '.multiple-choice input[checked]'
+    )
+
+    assert len(checked_radios) == 1
+    assert checked_radios[0]['value'] == expected_checked
+
+
+@pytest.mark.parametrize('post_value, international_sms_permission_expected_in_api_call', [
+    ('on', True),
+    ('off', False),
+])
 def test_switch_service_enable_international_sms(
-        logged_in_platform_admin_client,
-        service_one,
-        mocker,
+    client_request,
+    service_one,
+    mocker,
+    post_value,
+    international_sms_permission_expected_in_api_call,
 ):
     mocked_fn = mocker.patch('app.service_api_client.update_service_with_properties', return_value=service_one)
-
-    response = logged_in_platform_admin_client.get(
-        url_for('main.service_switch_can_send_international_sms', service_id=service_one['id'])
+    page = client_request.post(
+        'main.service_set_international_sms',
+        service_id=service_one['id'],
+        _data={
+            'enabled': post_value
+        },
+        _expected_redirect=url_for('main.service_settings', service_id=service_one['id'], _external=True)
     )
 
-    assert response.status_code == 302
-    assert response.location == url_for('main.service_settings', service_id=service_one['id'], _external=True)
-    assert 'international_sms' in mocked_fn.call_args[0][1]['permissions']
+    if international_sms_permission_expected_in_api_call:
+        assert 'international_sms' in mocked_fn.call_args[0][1]['permissions']
+    else:
+        assert 'international_sms' not in mocked_fn.call_args[0][1]['permissions']
+
     assert mocked_fn.call_args[0][0] == service_one['id']
 
 
-def test_switch_service_disable_international_sms(
-        logged_in_platform_admin_client,
-        service_one,
-        mocker,
-):
-    service_one['permissions'] = ['international_sms']
-    mocked_fn = mocker.patch('app.service_api_client.update_service_with_properties', return_value=service_one)
-
-    response = logged_in_platform_admin_client.get(
-        url_for('main.service_switch_can_send_international_sms', service_id=service_one['id'])
-    )
-
-    assert response.status_code == 302
-    assert response.location == url_for('main.service_settings', service_id=service_one['id'], _external=True)
-    assert mocked_fn.call_args == call(service_one['id'], {"permissions": []})
-
-
 def test_set_new_inbound_api_and_valid_bearer_token_calls_create_inbound_api_endpoint(
         logged_in_platform_admin_client,
         service_one,
@@ -1466,21 +1485,6 @@ def test_cant_resume_active_service(
 
 
 @pytest.mark.parametrize('endpoint, permissions, expected_p', [
-    (
-        'main.service_set_international_sms',
-        ['sms'],
-        (
-            'Sending text messages to international phone numbers is '
-            'an invitation‑only feature.'
-        )
-    ),
-    (
-        'main.service_set_international_sms',
-        ['sms', 'international_sms'],
-        (
-            'Your service can send text messages to international phone numbers.'
-        )
-    ),
     (
         'main.service_set_letters',
         [],