KB: How to recover from a corrupt / bad keeper snapshot

[Algunenano]

We should have a guide of things to document how to recover from a bad keeper snapshot.

We should cover:

• How will the problem manifest
• What's a snapshot and where to find them.
• Possible strategies for recovery and what each of them means

Once published, we should provide a link to this guide in the CH error message

[gingerwizard]

@DerekChia do you have anything here we can reuse?