Use GitHub Actions (#1005)

* Initial version of release workflow using GitHub Actions

Add release workflow using GitHub Actions to replace the current Azure
DevOps pipeline. Currently the same functionality is implemented. This
uses multiple builds in parallel to make better use of CPU resources.

Remove Azure DevOps pipeline.

* Add GitHub Actions workflow for pull-request checks

Lint Dockerfile and shell scripts when PRs are opened.

* Use multiple runners in parallel

Buildroot has stretches where CPU resources are not fully utilized.
Spawn multiple builds accross builders to increase load. Also sort them
by architecture to maximize ccache hit rate.

* Checkout before validate version

.github/workflows/pr-checks.yml

@@ -0,0 +1,20 @@
+# Home Assistant Operating System pull-request checks
+
+name: PR checks
+
+on: [pull_request]
+
+jobs:
+  linters:
+    runs-on: ubuntu-20.04
+    steps:
+    - name: Check out code
+      uses: actions/checkout@v1
+    - name: Check Dockerfile
+      uses: brpaz/hadolint-action@v1.1.0
+      with:
+        dockerfile: Dockerfile
+    - name: Check shell scripts
+      uses: ludeeus/action-shellcheck@1.0.0
+      with:
+        ignore: "buildroot"