Document what features are broken when db_key_base is lost
What does this MR do?
GitLab recently went on a drive to encrypt more database columns with
db_key_base. This is good, but it does mean that the effects of losing that key are more wide-ranging than they used to be.
Add some documentation that covers the features that are broken when this key is lost, and correct a few minor things about the existing "how to delete the useless encrypted data" example.
What are the relevant issue numbers?
Closes #57690 (closed)