Create and configure mutation tests

In order to make our unit tests more robust, let's configure mutation tests phase in CI. Prior to configuring them, we need to investigate the area - what are the options and what the best of them.
Note, that if mutation tests take too long to run (like 20mins), we need to create a separate CI build for them. If it's still in scope of 5 mins, then we can leave them in the same Unit Tests build.