DR: detect if a command is run without sudo privileges

Description

While testing DR, I ran the following command gitlab-ctl replicate-geo-database --host=primary and got this error message

---------------------------------------------------------------
WARNING: Make sure this script is run from the secondary server
---------------------------------------------------------------

This script will disable you local PostgreSQL database and start
a backup/restore from the primary node at 'primary'

*** You have 60 seconds to hit CTRL-C ***

* Stopping PostgreSQL and all GitLab services
[ERROR] Failed to execute: gitlab-ctl stop

It took me a while to figure out what I did wrong when in fact, I ran the command without being sudo.

Proposal

If during the setup of DR, we run a command without sudo, we should detect it and raise a proper warning.