CLC-4181 API to let superusers delete specific cache entries

https://jira.ets.berkeley.edu/jira/browse/CLC-4181

This will assist our standard upgrade procedure and should also help when diagnosing or working around certain production issues.
Ops may want to audit the usage of these endpoints for security reasons. I think this should log at WARN level like the other methods -- and the message should be more explicit that it was an a la carte cache deletion.