Feature/devcontainer

[pnoltes]

This PR introduces a Development Container setup.

Development Container:

A development container (or dev container for short) allows you to use a container as a full-featured development environment. It can be used to run an application, to separate tools, libraries, or runtimes needed for working with a codebase, and to aid in continuous integration and testing. Dev containers can be run locally or remotely, in a private or public cloud, in a variety of supporting tools and editors.

Source https://containers.dev

I think the development container setup is nicer that our current containers dir, because the development container is based on a specification and is currently already supported in Clion and VSCode.

I tried building and debugging individual tests using a dev container in CLion and VSCode and both worked for me.
IMO the support for dev containers work better in VSCode. Also - if I am correct - VSCode has now a better CMake support and combined with the C++ TestMate plugin I think I will starting using VSCode more.

[pnoltes]

@rlenferink Could you have a look and see if the devcontainer setup works for you?

If you agree I would like to remove the container dir and gitpod badge in favor for the devcontainer setup.