ci: add action to mark new issues for triage

.github/workflows/opened-issues-triage.yml

+name: Mark new issue for triage
+
+on:
+  issues:
+    types: [opened]
+
+jobs:
+  needs-triage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-ecosystem/action-add-labels@v1
+        with:
+          labels: needs triage