ci: enable VOXL2 CI builds with private Docker container

Remove modalai_voxl2 and qurt from CI exclusion lists and add
container overrides to use the private ghcr.io/px4/px4-dev-voxl2
image which contains the Qualcomm Hexagon SDK.

- Add voxl2 build group with x64 runner for cross-compilation
- Add GHCR credentials to workflow for private container pull
- Add packages:read permission to workflow
- Auto-build libfc_sensor.so stub during cmake configure
- Handle missing .px4/.elf gracefully in artifact packaging

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/build_all_targets.yml

@@ -29,6 +29,7 @@ concurrency:
 permissions:
   contents: write
   actions: read
+  packages: read
 
 jobs:
   group_targets:
@@ -94,6 +95,9 @@ jobs:
       fail-fast: false
     container:
       image: ${{ matrix.container }}
+      credentials:
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
     steps:
       - uses: runs-on/action@v2
       - uses: actions/checkout@v4