add dependabot_automerge.yml (#40)

(cherry picked from commit 0cf92fb)

Bump @slack/web-api from 6.9.1 to 7.0.2

Bumps [@slack/web-api](https://github.com/slackapi/node-slack-sdk) from 6.9.1 to 7.0.2.
- [Release notes](https://github.com/slackapi/node-slack-sdk/releases)
- [Commits](https://github.com/slackapi/node-slack-sdk/compare/@slack/[email protected]...@slack/[email protected])

---
updated-dependencies:
- dependency-name: "@slack/web-api"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/dependabot_automerge.yml

@@ -0,0 +1,13 @@
+name: Dependabot Workflow
+on:
+  pull_request_target
+
+jobs:
+  set-token:
+    runs-on: ubuntu-latest
+    if: ${{ github.actor == 'dependabot[bot]' }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          token: ${{ secrets.NPM_TOKEN }}