SWPROT-8953: ci: github: Add rootfs action

Origin: SiliconLabs/UnifySDK#50
Forwarded: #5
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

.github/workflows/build-rootfs.yml

@@ -0,0 +1,43 @@
+# YAML -*- mode: yaml; tab-width: 2; indent-tabs-mode: nil; coding: utf-8 -*-
+---
+name: Build in rootfs for arch
+
+on:  # yamllint disable-line rule:truthy
+  push:
+    tags:
+      - '*'
+jobs:
+  build:
+    runs-on: ubuntu-24.04
+    strategy:
+      matrix:
+        arch:
+          - amd64
+          - arm64
+    steps:
+      - uses: actions/checkout@v4.1.1
+        with:
+          fetch-depth: 0
+      - id: describe
+        name: Describe HEAD
+        run: >-
+          echo "describe=$(git describe --tags --always || echo 0)"
+          | tee $GITHUB_OUTPUT
+      - name: Setup and build
+        run: |
+          ARCH=${{ matrix.arch }} ./scripts/build-rootfs.sh
+      - name: Upload artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          # yamllint disable-line rule:line-length
+          name: ${{ github.event.repository.name }}-${{ steps.describe.outputs.describe }}-${{ matrix.arch }}
+          path: build/dist/
+      - name: Upload Release Asset
+        id: upload-release-asset
+        uses: softprops/action-gh-release@v2
+        if: startsWith(github.ref, 'refs/tags/')
+        with:
+          files: build/dist/*
+          # yamllint disable-line rule:line-length
+          # TODO: Sign asset: https://github.com/softprops/action-gh-release/issues/580#2025
+