docs(backup): comment on TakeBackupCommand.executeInSequence=false

Per Daan's review on PR #12847, document inline why we return false from
executeInSequence — the same reasoning previously only given in the PR
thread. The comment explains the design intent (parallel dispatch with
DeleteBackupCommand) and the safety case (per-VM on-NAS paths + per-script
NFS mount lifecycle).

Author: jmsperu

core/src/main/java/org/apache/cloudstack/backup/TakeBackupCommand.java

@@ -89,6 +89,12 @@ public void setVolumePaths(List<String> volumePaths) {
 
     @Override
     public boolean executeInSequence() {
+        // Returning false lets the KVM agent dispatch this command in parallel with
+        // other backup commands (notably DeleteBackupCommand). A long-running snapshot
+        // copy must not block a concurrent delete on a different VM's backup. Safe
+        // because each backup operates on its own on-NAS path (named after the VM
+        // uuid + timestamp) and the NFS mount lifecycle is per-script-invocation,
+        // not shared — so there is no path-level contention between parallel runs.
         return false;
     }
 }