Add replace_original/delete_original to WebhookClient (async/sync)

Add functionality to allow updating a message when using the WebhookClient by passing replace_original=true to the API.

Requirements

Currently it is only possible to send a new message using the WebhookClient. The Slack API offers the option to include a boolean replace_original flag that will then update the original message instead of posting a new message. It would be great if we could add a similar WebClient.chat_update method to the WebhookClient. Some PoC code of what this could look like:

def chat_update(
    self,
    *,
    text: Optional[str] = None,
    attachments: Optional[List[Union[Dict[str, any], Attachment]]] = None,
    blocks: Optional[List[Union[Dict[str, any], Block]]] = None,
    headers: Optional[Dict[str, str]] = None,
) -> WebhookResponse:
    """Performs a Slack API request and returns the result.
    :param text: the text message (even when having blocks, setting this as well is recommended as it works as fallback)
    :param attachments: a collection of attachments
    :param blocks: a collection of Block Kit UI components
    :param headers: request headers to append only for this request
    :return: API response
    """
    return self.send_dict(
        body={
            "text": text,
            "attachments": attachments,
            "blocks": blocks,
            "replace_original": True,
        },
        headers=headers,
    )

[Greenwolf]

+1 for adding this functionality, it would be really useful!

[alextriaca]

Makes sense. I guess the WebhookClient will only ever be dealing with a single message so treating it as different sounds good. Honestly just adding the replace_original flag will clean things up for me so appreciate you taking this on!