docker: Introduce Dockerfile to build Actuation demo

Add a Dockerfile that packages cmake and Zephyr dependencies. By
default the docker build builts for 'aarch64'. Pass
'--build-arg BUILD_ARCH=x86_64' during docker build to build
for 'x86_64' development platforms.

Signed-off-by: Vineeth Raveendran <vineeth.raveendran@arm.com>