Upload complete source tarball as release asset

Contrary to auto-generated release tarballs, this one includes all
submodules such that operating system infrastructure gets a complete
source tree wihtout having to fetch submodules themself.

Add "-full" between name and version to distinguish the two tarballs.

The token needs read/write permissions to clone the repository and
upload assets to existing releases, respectively.

Fixes #274

Signed-off-by: Klemens Nanni <[email protected]>

.github/workflows/release-tarball.yml

@@ -0,0 +1,35 @@
+name: Release Tarball
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  upload-release-tarball:
+    name: upload complete source code for release
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: checkout tagged release recursively incl. submodules
+      uses: actions/checkout@v3
+      with:
+        submodules: recursive
+
+    - name: set environment variables
+      run: |
+        NAME="${{ github.repository }}"
+        NAME="${NAME#*/}-full-${{ github.ref_name }}"
+        FILE="./${NAME}.tar.gz"
+        echo "NAME=${NAME}" >> "${GITHUB_ENV}"
+        echo "FILE=${FILE}" >> "${GITHUB_ENV}"
+
+    - name: create compressed tarball with git-archive(1)
+      uses: qmonnet/git-archive-all-action@v1
+      with:
+        prefix: ${{ format('{0}/', env.NAME) }}
+        output-files: ${{ env.FILE }}
+
+    - name: upload static release asset
+      uses: svenstaro/upload-release-action@v2
+      with:
+        file: ${{ env.FILE }}