ci: Add docker based test framework

* Add documentation
* Add .dockerignore: minimize docker context size to improve speed
* Add Makefile: to easily run various docker stages
* Add a CMake sample project to check CMake install rules

ci/doc/generate_image.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+set -ex
+
+rm -f ./*.svg ./*.png
+for i in *.dot; do
+  plantuml -Tsvg "$i";
+done