Packaging: Update marker used to allow ELASTIC_PASSWORD (#37243)

This commit updates the file docker's entrypoint script looks for when
deciding to process the ELASTIC_PASSWORD env var. The x-pack subdir
of bin no longer exists in 7.0, where the backcompat layer for x-pack
script locations was removed.

closes #37240

distribution/docker/src/docker/bin/docker-entrypoint.sh

@@ -75,7 +75,7 @@ done < <(env)
 # will run in.
 export ES_JAVA_OPTS="-Des.cgroups.hierarchy.override=/ $ES_JAVA_OPTS"
 
-if [[ -d bin/x-pack ]]; then
+if [[ -f bin/elasticsearch-users ]]; then
   # Check for the ELASTIC_PASSWORD environment variable to set the
   # bootstrap password for Security.
   #