Add CI support for testing and building docker image

[scp93ch]

We need a CI configuration that executed the test suite (via gradle). It should execute on merge into dev and main. It should be possible to run the tests manually on other branches.

In addition we should extract the test results and test coverage as build artifacts.

We also want to build a docker image for the system-modeller, with the software deployed in Tomcat.

[scp93ch]

Still need to build docker image.