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
Each Slack webhook token can be pre-configured to use a specific channel, username and
    icon. You can override these defaults in this hook.
    :param http_conn_id: connection that has Slack webhook token in the extra field
    :type http_conn_id: str
    :param webhook_token: Slack webhook token
    :type webhook_token: str
    :param message: The message you want to send on Slack
    :type message: str
    :param attachments: The attachments to send on Slack. Should be a list of
        dictionaries representing Slack attachments.
    :type attachments: list
    :param blocks: The blocks to send on Slack. Should be a list of
        dictionaries representing Slack blocks.
    :type blocks: list
    :param channel: The channel the message should be posted to
    :type channel: str
    :param username: The username to post to slack with
    :type username: str
    :param icon_emoji: The emoji to use as icon for the user posting to Slack
    :type icon_emoji: str
    :param icon_url: The icon image URL string to use in place of the default icon.
    :type icon_url: str
    :param link_names: Whether or not to find and link channel and usernames in your
        message
    :type link_names: bool
    :param proxy: Proxy to use to make the Slack webhook call
    :type proxy: str
    """
    
    def __init__(