purge command should give feedback if can not be executed

[islamaliev]

In normal mode:

$ defradb client purge
Error: run this command again with --force if you really want to purge all data

$ defradb client purge --force

There is no output as if it was successful.
Node's logs:

Oct 15 13:57:19.878 INF cli Received purge event; restarting...
Oct 15 13:57:19.878 ERR cli failed to purge $err="cannot purge database when development mode is disabled"

Client's CLI should output that purge can not be performed instead of letting it through and silently failing.