[Feat]: improvements to slack integration

[andrewm4894]

Problem

i think it would be more nice if our slack integration would use threads for each alert instead of posting fresh new messages for each status change. https://api.slack.com/messaging/sending#threading

Description

eg 2nd msg here should have been added as a reply to first in the thread.

so any time a alert goes to warning or critical we create a new message and any time the alert goes back down we send the recovery message to the thread.

if we wanted to get really fancy we'd actually update the original message too.
Metaplane is a data observability app we had been using and thier slack integration is best i have seen

so i end up with one slack msg per alert, a thread with updates, and the original msg itself updates if/when alert is closed automatically.
end result being as compact as possible stream of alerts in my slack channel that i can quickly scan to see which ones are closed and which ones are still open.

Importance

nice to have

Value proposition

1. a really nice slack integration

Proposed implementation

No response