Note: This doesn't change the occurences in the Zapier integration doc,
since they refer to pieces of the UI in Zapier, which may still be using
the "Stream" terminology.
Due to the channel_map_to_topics URL parameter in the Slack webhook,
it was not migrated to use the check_send_webhook_message.
By using check_send_webhook_message, any topic parameter in the
webhook URL will be prioritized over mapping Slack channels to
topics, e.g. when channel_map_to_topics is true. This is because
the default behaviour for incoming webhooks is to send a default
topic as a parameter to check_send_webhook_message in case there
is no topic specified in the URL.
In contrast, we can override the stream passed in the URL when
channel_map_to_topics is false by passing the Slack channel name
to check_send_webhook_message. The default behaviour for incoming
webhooks is to send a direct message if there is no specified
stream in the URL, so a default stream is not generally passed
to check_send_webhook_message.
Fixes#27601.
Updates the Slack integration page to not describe adding a stream
or topic parameter to the URL query since that's not supported by
the current integration implementation.
Updates the Slack-compatible webhook integration page to have the
extra notes about the integration at the top of the page. Also,
removes the reference to a screenshot of the webhook since there
isn't one.
markdown-include is GPL licensed.
Also, rewrite it as a block processor, so that it works correctly
inside indented blocks.
Signed-off-by: Anders Kaseorg <anders@zulip.com>