Document "persistence volume is not unlocked"
From #11649 (closed), people are searching for this and we should add this error message somewhere in the doc about the Persistent Storage.
What I see in search logs is:
"persistence volume on /dev/sdb is not unlocked"
Which differs from what I see in:
"Persistence volume is not unlocked."
We should first check what the actual error message is when opening the Persistent Storage settings with a locked Persistent Storage.