feat(ci): upload release artifacts to Cloudflare R2 (#65)

After publishing to the GitHub Release, upload the built binaries to
the yellowjacket-releases R2 bucket for the download static site.

.github/workflows/build.yml

@@ -174,3 +174,13 @@ jobs:
             artifacts/release/yellowjacket-linux-amd64
             artifacts/release/yellowjacket-darwin-universal.app.zip
             artifacts/release/yellowjacket-windows-amd64.exe
+
+      - name: Upload to R2
+        uses: ryand56/r2-upload-action@v1
+        with:
+          r2-account-id: ${{ secrets.R2_ACCOUNT_ID }}
+          r2-access-key-id: ${{ secrets.R2_ACCESS_KEY_ID }}
+          r2-secret-access-key: ${{ secrets.R2_SECRET_ACCESS_KEY }}
+          r2-bucket: yellowjacket-releases
+          source-dir: artifacts/release
+          destination-dir: releases/${{ github.event.release.tag_name }}