ci: Add Label Commenter Action

https://github.com/peaceiris/actions-label-commenter

.github/label-commenter-config.yml

@@ -0,0 +1,32 @@
+labels:
+  - name: invalid
+    labeled:
+      issue:
+        body: Please follow the issue templates.
+        action: close
+  - name: forum
+    labeled:
+      issue:
+        body: |
+          Please ask questions about GitHub Actions or Hugo at the following forum.
+          - [GitHub Actions Community Forum](https://github.community/t5/GitHub-Actions/bd-p/actions)
+          - [Hugo Community Forum](https://discourse.gohugo.io/)
+        action: close
+  - name: wontfix
+    labeled:
+      issue:
+        body: This will not be worked on but we appreciate your contribution.
+        action: close
+    unlabeled:
+      issue:
+        body: This has become active again.
+        action: open
+  - name: duplicate
+    labeled:
+      issue:
+        body: This issue already exists.
+        action: close
+  - name: good first issue
+    labeled:
+      issue:
+        body: This issue is easy for contributing. Everyone can work on this.

.github/workflows/label-commenter.yml

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+name: Label Commenter
+
+on:
+  issues:
+    types:
+      - labeled
+      - unlabeled
+  # pull_request:
+  #   types:
+  #     - labeled
+  #     - unlabeled
+
+jobs:
+  comment:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: master
+
+      - name: Label Commenter
+        uses: peaceiris/actions-label-commenter@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          # config_file: .github/label-commenter-config.yml