Fix typo in obtaining a backtrace from all threads in gdb

Also add command to turn off pagination

[ci skip]

doc/administration/troubleshooting/sidekiq.md

@@ -147,7 +147,8 @@ bt
 To output a backtrace from all threads at once:
 
 ```
-apply all thread bt
+set pagination off
+thread apply all bt
 ```
 
 Once you're done debugging with `gdb`, be sure to detach from the process and