Add GitHub Action for automatic releases

Closes #5

.github/workflows/release.yml

@@ -0,0 +1,51 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*.*.*"
+
+jobs:
+  package:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install dependencies
+        run: npm ci
+      - name: Build packages
+        run: npm run package
+
+      # Create automatic draft release for pushes of tags, prefilled with all the important information.
+      # And since we have our files, let's attach them as well.
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v1
+        with:
+          draft: true
+          generate_release_notes: true
+          files: "web-ext-artifacts/*.zip"
+
+  release-firefox:
+    runs-on: ubuntu-latest
+    needs: package
+    steps:
+      - name: Download assets for release
+        run: >
+          gh release download ${{ github.ref }} --archive zip --dir assets
+          gh release download ${{ github.ref }} --pattern "*firefox*" --dir assets
+      - uses: browser-actions/release-firefox-addon@v0.1.3
+        with:
+          addon-id: "protoots"
+          addon-path: "assets/protoots-firefox.zip"
+          source-path: "assets/ProToots-${{ github.ref }}.zip"
+          approval-note: |
+            The source code requires Node.js 18 or newer. To generate the source code, run:
+
+            npm ci
+            npm run package
+
+            To check it's functionality, you can enable it on any Mastodon page, such as: https://mastodon.social/public
+          license: OSL-3.0
+          auth-api-issuer: ${{ secrets.FIREFOX_AUTH_API_ISSUER }}
+          auth-api-secret: ${{ secrets.FIREFOX_AUTH_API_SECRET }}