private String configureServiceContainerLabels(String existingEnvFlagKey) {
        String internalMarkerFlags = internalMarkerLabels();
        String existingFlags = getEnvMap().get(existingEnvFlagKey);
        if (existingFlags != null) {
            internalMarkerFlags = existingFlags + " " + internalMarkerFlags;
        }
        return "\"" + internalMarkerFlags + "\"";
    }
Configure the LocalStack container to include the default testcontainers labels on all spawned lambda containers
Necessary to properly clean up lambda containers even if the LocalStack container is killed before it gets the
chance.
@return the lambda container labels as a string
modules/localstack/src/main/java/org/testcontainers/containers/localstack/LocalStackContainer.java