Run containers with --init by default to avoid leaking zombie processes.

People running containers manually usually run with pid 1 being a
$SHELL, in which case waiting for child termination is something
implemented already as it's the core job of a $SHELL. However with this
jenkins plugin the command run is usually "cat" on Linux, which doesn't
wait at all for children. To have in jenkins a situation a bit like
during interactive container experience, start containers with --init
so zombie processes are correctly reaped.

Author: Romain-Geissler-1A

src/main/java/org/jenkinsci/plugins/docker/workflow/client/DockerClient.java

@@ -116,7 +116,7 @@ public DockerClient(@NonNull Launcher launcher, @CheckForNull Node node, @CheckF
     public String run(@NonNull EnvVars launchEnv, @NonNull String image, @CheckForNull String args, @CheckForNull String workdir, @NonNull Map<String, String> volumes, @NonNull Collection<String> volumesFromContainers, @NonNull EnvVars containerEnv, @NonNull String user, @NonNull String... command) throws IOException, InterruptedException {
         ArgumentListBuilder argb = new ArgumentListBuilder();
 
-        argb.add("run", "-t", "-d");
+        argb.add("run", "-t", "-d", "--init");
 
         // Username might be empty because we are running on Windows
         if (StringUtils.isNotEmpty(user)) {