pt-mongodb-query-digest doesn't work on standalone server

Description:

pt-mongodb-query-digest fails when we run it against a standalone instance of MongoDB and returns "Cannot get profiler status: sharding not enabled"
 
Environment:
Linux ubuntu-focal 5.4.0-125-generic
Percona Server for MongoDB server version: v4.0.28-23
pt-mongodb-query-digest Version 3.4.0
 
How to reproduce:
vagrant@ubuntu-focal:~$ pt-mongodb-query-digest localhost:27017/admin -uadmin -padmin123 -d=zelmar
ERRO[0000] Cannot get profiler status: sharding not enabled
 
 
Suggested fix:
Allow pt-mongodb-query-digest to work on a standalone instance of MongoDB.