Split off the DockerClientFactory from this library

Most times I play with other Docker/Java libraries than TestContainers I end up in a world of dependency or configuration hell. It seems like one of the biggest reasons for this is this library's DockerClientFactory class, which does a really excellent job of inspecting the environment and choosing the best way of running Docker on the local machine with very little user intervention.

This is particularly instrumental when trying to convince other users to adopt Docker-based unit testing—if it doesn't "just work" (as it does!), skeptical developers are prone to reject the whole thing.

Therefore, I think that this class and its supporting cast should perhaps be split off into a separate package or merged upstream so that more people and projects can benefit this most commendable work. I know I'd certainly use it!

Start by reading core/src/main/java/org/testcontainers/DockerClientFactory.java and identifying the supporting classes involved in environment inspection and Docker runtime selection. The issue proposes separating this functionality into its own package or merging it upstream, so first clarify the extraction boundary and integration target; done means the resulting functionality can benefit other Docker/Java projects without the current dependency or configuration conflicts.