github: Add action for checking PR in developers forks

Enable github actions that build any branches using docker along helper script.
To avoid bringing more ambiguity or complexity
most tasks are isolated at lowerlevel (in helper for cmake).

Relate-to: https://github.com/rzr/wisun-br-linux/actions/runs/11687351317/job/32545249359
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

.github/workflows/build.yml

@@ -0,0 +1,19 @@
+# YAML -*- mode: yaml; tab-width: 2; indent-tabs-mode: nil; coding: utf-8 -*-
+# SPDX-License-Identifier: LicenseRef-MSLA
+# SPDX-Copyright-Text: (c) 2024 Silicon Laboratories Inc. (www.silabs.com)
+---
+name: Docker Image CI
+
+on:  # yamllint disable-line rule:truthy
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4.1.1
+        with:
+          fetch-depth: 0
+      - name: Build Docker image from sources
+        run: docker build .