chore: Add slack notification github action (#459)

*Issue #, if available:*

*Description of changes:*

- Add slack notification github action.
- The secret key has been set up.

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copy, and redistribute this contribution, under the terms of your
choice.

Co-authored-by: Alex Wang <wangyb@amazon.com>

Author: wangyb-A

.github/workflows/notify_slack.yml

@@ -0,0 +1,39 @@
+name: Slack Notifications
+
+on:
+  issues:
+    types: [opened, reopened]
+  pull_request_target:
+    types: [opened, reopened]
+
+permissions: {}
+
+jobs:
+  notify:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Send issue notification to Slack
+        if: github.event_name == 'issues'
+        uses: slackapi/slack-github-action@v2.1.1
+        with:
+          webhook: ${{ secrets.SLACK_WEBHOOK_URL_ISSUE }}
+          webhook-type: incoming-webhook
+          payload: |
+            {
+              "action": "${{ github.event.action }}",
+              "issue_url": "${{ github.event.issue.html_url }}",
+              "package_name": "${{ github.repository }}"
+            }
+
+      - name: Send pull request notification to Slack
+        if: github.event_name == 'pull_request_target'
+        uses: slackapi/slack-github-action@v2.1.1
+        with:
+          webhook: ${{ secrets.SLACK_WEBHOOK_URL_PR }}
+          webhook-type: incoming-webhook
+          payload: |
+            {
+              "action": "${{ github.event.action }}",
+              "pr_url": "${{ github.event.pull_request.html_url }}",
+              "package_name": "${{ github.repository }}"
+            }