Note Ghost user and refer to user deletion documentation

What does this MR do?

Upon user or account deletion we should some guidance regarding the consequences of deletion. This guidance needed revising after introducing the Ghost user which will adopt the deleted user's resources.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

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

What are the relevant issue numbers?

Closes #31383 (closed)