Include ldap troubleshooting steps for blocked users

What does this MR do?

Based on https://gitlab.zendesk.com/agent/tickets/26154

cc/ @dblessing @stanhu @balameb

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together