Hello,

Slack has released updates to its library and we can start using it for it. 

We especially like one change.

> slack_sdk has no required dependencies. This means aiohttp is no longer automatically resolved.

I've looked through the documentation and it doesn't look like a difficult task, but I think it's still worth testing.
More info: https://slack.dev/python-slack-sdk/v3-migration/index.html#from-slackclient-2-x

Best regards,
Kamil Breguła
airflow/providers/slack/hooks/slack.py
"""
    Creates a Slack connection, to be used for calls. Takes both Slack API token directly and
    connection that has Slack API token. If both supplied, Slack API token will be used.
    Exposes also the rest of slack.WebClient args
    Examples:
    .. code-block:: python
        # Create hook
        slack_hook = SlackHook(token="xxx")  # or slack_hook = SlackHook(slack_conn_id="slack")
        # Call generic API with parameters (errors are handled by hook)
        #  For more details check https://api.slack.com/methods/chat.postMessage
        slack_hook.call("chat.postMessage", json={"channel": "#random", "text": "Hello world!"})
        # Call method from Slack SDK (you have to handle errors yourself)
        #  For more details check https://slack.dev/python-slackclient/basic_usage.html#sending-a-message
        slack_hook.client.chat_postMessage(channel="#random", text="Hello world!")
    :param token: Slack API token
    :type token: str
    :param slack_conn_id: connection that has Slack API token in the password field
    :type slack_conn_id: str
    :param use_session: A boolean specifying if the client should take advantage of
        connection pooling. Default is True.
    :type use_session: bool
    :param base_url: A string representing the Slack API base URL. Default is
        ``https://www.slack.com/api/``
    :type base_url: str
    :param timeout: The maximum number of seconds the client will wait
        to connect and receive a response from Slack. Default is 30 seconds.
    :type timeout: int
    """
    def __init__(