Synchronization/solidification integration test (#346)

* Introduce concept of networks

* Adjust tests to use flexible Docker networks

* Adjust test execution workflow

* Separately build GoShimmer Docker image

* Generate identities to create containers from seeds

* Move Docker network functionality

* Add comments and docs

* Update readme

* Update readme

* Add synchronization test

* Adjust to merge changes

* Add additional checks including solidification check

* Adjust to naming changes

* Simplify ids seen check

* Address PR comments