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!

まず core/src/main/java/org/testcontainers/DockerClientFactory.java を読み、環境の検査と Docker runtime の選択に関係するサポートクラスを特定します。issue では、この機能を独自の package に分離するか upstream に統合することを提案しているため、最初に抽出範囲と統合先を明確にします。完了の基準は、現在の依存関係または設定の競合なしに、結果として得られる機能を他の Docker/Java プロジェクトでも利用できることです。