server-pgsql/ubuntu/Dockerfile: Install sudo package and allow zabbix user to run sudo

[bboerner]

Using docker-compose_v3_ubuntu_pgsql_latest.yaml pinging a host or "detect operating system" will result in

sh: 1: sudo: not found

Adding sudo package then the error is,

sudo: a terminal is required to read the password; either use the -S option to read from standard input or configure an askpass helper
sudo: a password is required

See #1741.