[dependabot] add slack alerts (#280)

Enables dependabot slack alerts for `0x-settler`

@0xProject/platform-engineering

.github/workflows/dependabot-slack-alerts.yml

@@ -0,0 +1,22 @@
+name: Dependabot Slack alerts
+
+permissions:
+  contents: read
+  security-events: read
+
+on:
+  # TODO: enable hourly run once tested
+  #schedule:
+  #  - cron: '0 * * * *'
+  workflow_dispatch:
+jobs:
+  notify-vulnerabilites:
+    runs-on: ubuntu-latest
+    steps:
+      # Latest version available at: https://github.com/kunalnagarco/action-cve/releases
+      - name: Notify Vulnerabilities
+        uses: kunalnagarco/[email protected]
+        with:
+          severity: high,critical
+          token: "${{ secrets.DEPENDABOT_GITHUB_TOKEN }}"
+          slack_webhook: "${{ secrets.DEPENDABOT_SLACK_WEBHOOK }}"