ci: notify #moab-primary-oncalls on Monday e2e status

Add a workflow_run listener on the scheduled "E2E Tests (Full Suite)"
run that fires a Slack webhook-trigger payload with pass/fail status
and the @moab-primary-oncalls subteam mention (<!subteam^S0A1Q6WN8JX>).

Gated on github.event.workflow_run.event == 'schedule' so manual
dispatches and pushes don't page oncall. Reuses SLACK_WEBHOOK_URL; the
Slack-side workflow needs a new branch keyed on notification_type to
format this payload differently from the issue-opened notification.

Author: tejaskash

.github/workflows/slack-e2e-status-notification.yml

@@ -0,0 +1,31 @@
+name: Slack E2E Status Notification
+
+on:
+  workflow_run:
+    workflows: ['E2E Tests (Full Suite)']
+    types: [completed]
+
+permissions:
+  contents: read
+
+jobs:
+  notify-slack:
+    # Only notify on the scheduled Monday run, not manual dispatches or push runs
+    if: github.event.workflow_run.event == 'schedule'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Send E2E status to Slack
+        uses: slackapi/slack-github-action@v2.1.1
+        with:
+          webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
+          webhook-type: webhook-trigger
+          payload: |
+            notification_type: "e2e_status"
+            status: "${{ github.event.workflow_run.conclusion }}"
+            status_emoji: "${{ github.event.workflow_run.conclusion == 'success' && ':white_check_mark:' || ':x:' }}"
+            status_text: "${{ github.event.workflow_run.conclusion == 'success' && 'PASSED' || 'FAILED' }}"
+            mention: "<!subteam^S0A1Q6WN8JX>"
+            run_url: "${{ github.event.workflow_run.html_url }}"
+            repository: "${{ github.repository }}"
+            started_at: "${{ github.event.workflow_run.run_started_at }}"
+            workflow_name: "${{ github.event.workflow_run.name }}"