Switch to using incoming webhook for posting to slack
The current method requires a new Slack App to be created and approved. This switches back to the old method of using incoming-webhooks. See: https://gitlab.com/gitlab-com/business-ops/change-management/-/issues/2#note_307033476
Related to https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/372
Edited by Sanad Liaquat