Currently `SlackWebhookHook` gets the token from `extra` but it would be more secure and intuitive to have it in password.

https://github.com/apache/airflow/blob/4fb5c017fe5ca41ed95547a857c9c39efc4f1476/airflow/providers/slack/hooks/slack_webhook.py
tests/providers/slack/hooks/test_slack_webhook.py
hook = SlackWebhookHook(webhook_token=self.expected_url)
        try:
            hook.execute()
        except MissingSchema:
            pass
        mock_request.assert_called_once_with(
            self.expected_method, self.expected_url, headers=mock.ANY, data=mock.ANY
        )
        mock_request.reset_mock()
    @mock.patch('requests.Session')
    @mock.patch('requests.Request')
    def test_url_generated_by_http_conn_id_and_endpoint(self, mock_request, mock_session):
        hook = SlackWebhookHook(http_conn_id='slack-webhook-host', webhook_token='B000/XXX')
        try:
            hook.execute()
        except MissingSchema:
            pass
        mock_request.assert_called_once_with(
            self.expected_method, self.expected_url, headers=mock.ANY, data=mock.ANY
        )
        mock_request.reset_mock()