Use Release Drafter as GitHub action (#166)

.github/release-drafter.yml

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+# Config for https://github.com/release-drafter/release-drafter
+name-template: 'sbt-site $NEXT_PATCH_VERSION'
+tag-template: 'v$NEXT_PATCH_VERSION'
+change-template: '- $TITLE #$NUMBER by @$AUTHOR'
+template: |
+  ## Changes
+
+  $CHANGES
+
+  ## Contributors
+
+  $CONTRIBUTORS

.github/workflows/release-drafter.yml

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+name: Release Drafter
+
+on:
+  push:
+    # branches to consider in the event; optional, defaults to all
+    branches:
+      - develop
+
+jobs:
+  update_release_draft:
+    runs-on: ubuntu-latest
+    steps:
+      # Drafts your next Release notes as Pull Requests are merged
+      # https://github.com/raboof/release-drafter/releases
+      # fork of https://github.com/release-drafter/release-drafter/releases
+      - uses: raboof/release-drafter@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}