GHA: add copyright action

Author: junghans

.github/workflows/copyright.yml

@@ -0,0 +1,40 @@
+name: Copyright
+on:
+  issue_comment:
+    types: [created]
+jobs:
+  edit:
+    name: Copyright
+    if: ${{ github.event.comment.body == '@votca-bot copyright' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check if message comes from PR
+        uses: octokit/request-action@v2.x
+        id: issue_info
+        with:
+          route: GET /repos/:repository/issues/:pull_number
+          repository: ${{ github.repository }}
+          pull_number: ${{ github.event.issue.number }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - name: Get PR info
+        if: ${{ fromJSON(steps.issue_info.outputs.data).pull_request }}
+        uses: octokit/request-action@v2.x
+        id: pr_info
+        with:
+          route: GET /repos/:repository/pulls/:pull_number
+          repository: ${{ github.repository }}
+          pull_number: ${{ github.event.issue.number }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - name: Checkout head branch from PR
+        if: ${{ fromJSON(steps.issue_info.outputs.data).pull_request }}
+        uses: actions/checkout@v2.2.0
+        with:
+          repository: ${{ fromJSON(steps.pr_info.outputs.data).head.repo.full_name }}
+          ref: ${{ fromJSON(steps.pr_info.outputs.data).head.ref }}
+          fetch-depth: 0
+          token: ${{ secrets.VOTCA_BOT_TOKEN }}
+      - name: Create and commit copyright updates
+        if: ${{ fromJSON(steps.issue_info.outputs.data).pull_request }}
+        uses: votca/actions/copyright@master
+        with:
+          base: ${{ fromJSON(steps.pr_info.outputs.data).base.sha }}