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
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import json
from typing import Optional
from airflow.exceptions import AirflowException
from airflow.providers.http.hooks.http import HttpHook
class SlackWebhookHook(HttpHook):
    """
    This hook allows you to post messages to Slack using incoming webhooks.
    Takes both Slack webhook token directly and connection that has Slack webhook token.
    If both supplied, http_conn_id will be used as base_url,
    and webhook_token will be taken as endpoint, the relative path of the url.