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
airflow/providers/slack/hooks/slack_webhook.py
"""Remote Popen (actually execute the slack webhook call)"""
        proxies = {}
        if self.proxy:
            
            proxies = {'https': self.proxy}
        slack_message = self._build_slack_message()
        self.run(
            endpoint=self.webhook_token,
            data=slack_message,
            headers={'Content-type': 'application/json'},
            extra_options={'proxies': proxies, 'check_response': True},
        )