Update validators to use is_message_too_long()

- update check_sms_content_char_count to use the SMSTemplate.is_message_too_long function, and updated the error message to align with the message returned by the admin app.
- Update the the code used by version 1 of the api to use the validate_template method.
  - I did find a couple of services still using the old api, however, this change should not affect them as I checked the messages being sent and they are not too long.
  - We will be sending a message to them to see if they can upgrade.
- Update the log message for authenication to include the URL - makes it easier to track if a service is using version 1 of the api.

tests/app/service/test_send_one_off_notification.py

@@ -294,8 +294,8 @@ def test_send_one_off_notification_raises_if_message_too_long(persist_mock, noti
     with pytest.raises(BadRequestError) as e:
         send_one_off_notification(service.id, post_data)
 
-    assert e.value.message == 'Content for template has a character count greater than the limit of {}'.format(
-        SMS_CHAR_COUNT_LIMIT)
+    assert e.value.message == f'Text messages cannot be longer than {SMS_CHAR_COUNT_LIMIT} characters. ' \
+                              f'Your message is {729} characters'
 
 
 def test_send_one_off_notification_fails_if_created_by_other_service(sample_template):