split: tell slack (#12874)

Also, change timing of nightly snapshot to work better with Canton.

CHANGELOG_BEGIN
CHANGELOG_END

ci/daily-snapshot.yml

@@ -4,7 +4,7 @@
 pr: none
 trigger: none
 schedules:
-- cron: "30 4 * * *"
+- cron: "0 1 * * *"
   displayName: Daily split snapshot
   branches:
     include:

ci/split-release-job.yml

@@ -91,6 +91,13 @@ jobs:
         ./ci/publish-artifactory.sh $(Build.StagingDirectory) $(release_tag) split
       env:
         AUTH: $(ARTIFACTORY_USERNAME):$(ARTIFACTORY_PASSWORD)
+    - bash: |
+        set -euo pipefail
+        # Note: this gets dev-env from the release commit, not the trigger commit
+        eval "$(./dev-env/bin/dade-assist)"
+        source $(bash-lib)
+        tell_slack "Split release \`$(release_tag)\` just pushed to Artifactory." \
+                   "$(Slack.ci-failures-daml)"
     - template: tell-slack-failed.yml
       parameters:
         trigger_sha: '$(trigger_sha)'