Slack files.upload Broken for New Slack Apps as of May 2024

[ESNewmanium]

Image uploads to Slack using ngalert.notifier.slack are no longer working as of May 2024. Slack API has deprecated this method and prevents newly created apps from using it. The Slack API responds with "method_deprecated" and the upload fails.

An example of an attempted image upload is below.

logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 t=2024-08-28T08:24:37.84186656-05:00 level=debug msg="Looks like we are using the Slack API, have set the Bearer token for this request"
logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 t=2024-08-28T08:24:38.095552788-05:00 level=debug msg="The request was successful"
logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 t=2024-08-28T08:24:38.096132436-05:00 level=debug msg="Uploadimg image" image=f58a0199-76ce-4169-8e2f-f3c544211250
logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 t=2024-08-28T08:24:38.096233945-05:00 level=debug msg="Sending multipart request to files.upload"
logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 t=2024-08-28T08:24:38.198886857-05:00 level=error msg="The request was unsuccessful" body="{\"ok\":false,\"error\":\"method_deprecated\"}" err=method_deprecated
logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 alert="Unexpected Container Restart[5a4c147][active]" t=2024-08-28T08:24:38.198943018-05:00 level=error msg="Failed to attach image to notification" error="failed to send request: failed to send request: method_deprecated"
logger=ngalert.notifier.slack notifierUID=e41965c3-d944-4377-b3fa-816762249833 t=2024-08-28T08:24:38.198961721-05:00 level=error msg="Failed to upload image" err="failed to send request: failed to send request: method_deprecated"