fix: improve nightly Docker build failure Slack notification (#22130)

Co-authored-by: Amp <amp@ampcode.com>

.changelog/fast-waves-smile.md

@@ -0,0 +1,4 @@
+---
+---
+
+Improved nightly Docker build failure Slack notification with more detailed formatting and context.

.github/workflows/docker.yml

@@ -117,6 +117,18 @@ jobs:
       - name: Slack Webhook Action
         uses: rtCamp/action-slack-notify@v2
         env:
-          SLACK_COLOR: ${{ job.status }}
-          SLACK_MESSAGE: "Failed run: https://github.com/paradigmxyz/reth/actions/runs/${{ github.run_id }}"
+          SLACK_COLOR: danger
+          SLACK_ICON_EMOJI: ":rotating_light:"
+          SLACK_USERNAME: "GitHub Actions"
+          SLACK_TITLE: ":rotating_light: Nightly Docker Build Failed"
+          SLACK_MESSAGE: |
+            The scheduled nightly Docker build failed.
+
+            *Commit:* `${{ github.sha }}`
+            *Branch:* `${{ github.ref_name }}`
+            *Run:* <https://github.com/paradigmxyz/reth/actions/runs/${{ github.run_id }}|View logs>
+
+            *Action required:* Re-run the workflow or investigate the build failure.
+          SLACK_FOOTER: "paradigmxyz/reth · docker.yml"
+          MSG_MINIMAL: true
           SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK_URL }}