Note praefect:replicas raketask in troubleshooting docs
What does this MR do?
The gitlab:praefect:replicas
rake task can be used to validate
repo state when Praefect is untrusted, but is not currently
mentioned in the Praefect troubleshooting docs.
This MR adds a reference to the raketask to make it more discoverable.
Edited by Will Chandler (ex-GitLab)