Proposal to add org.testcontainers=true label for ecosystem consistency

[walf443]

I would like to propose adding the org.testcontainers=true label by default to all containers started by the Rust implementation.

Currently, I manage Testcontainers using OnceCell in my Rust project. Occasionally, the cleanup process fails, leaving orphaned containers that I have to clean up manually.

docker kill $(docker ps -q --filter "label=org.testcontainers.managed-by=testcontainers")

While I can currently filter them using label=org.testcontainers.managed-by=testcontainers, other language implementations (such as Java and Go) typically use label=org.testcontainers=true for this purpose.

Adding this standard label would align the Rust version with the broader Testcontainers ecosystem. Moreover, since many AI agents and cleanup tools commonly suggest filtering by label=org.testcontainers=true, supporting this label would make the Rust implementation more intuitive and easier to manage across different environments.