Add workflow for dessant/support-requests

we're using the legacy github app right now.

.github/workflows/support.yml

@@ -0,0 +1,22 @@
+name: 'Manage support request issues'
+
+on:
+  issues:
+    types: [labeled, unlabeled, reopened]
+
+jobs:
+  support:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/support-requests@v2
+        with:
+          github-token: ${{ github.token }}
+          support-label:  "Support request"
+          issue-comment: >
+            Thanks, but this issue tracker is not intended for support requests. Please read the guidelines on [submitting an issue](https://github.com/pmmp/PocketMine-MP/blob/master/CONTRIBUTING.md#creating-an-issue).
+
+
+            [Docs](https://pmmp.rtfd.io) | [Discord](https://discord.gg/bmSAZBG) | [Forums](https://forums.pmmp.io)
+
+          close-issue: true
+          lock-issue: false