[baseimage]: add docker ps to the sudoer file (sonic-net#6604)

fixes sonic-net/sonic-utilities#1389

With the recent changes in sudoer files. The  show commands fails for the read-only users. 
The problem here is the 'docker ps' is failing in the function [get_routing_stack()](https://github.com/Azure/sonic-utilities/blob/8a1109ed30576f0287fcd98a4349617f7fb55700/show/main.py#L54) therefore all the CLI commands are failing.

Signed-off-by: Arvindsrinivasan Lakshmi Narasimhan <arlakshm@microsoft.com>

files/image_config/sudoers/sudoers

@@ -25,6 +25,7 @@ Cmnd_Alias      READ_ONLY_CMDS = /bin/cat /var/log/syslog*, \
                                  /usr/bin/docker exec bgp cat /etc/quagga/bgpd.conf, \
                                  /usr/bin/docker images *, \
                                  /usr/bin/docker ps *, \
+                                 /usr/bin/docker ps, \
                                  /usr/bin/lldpctl, \
                                  /usr/bin/sensors, \
                                  /usr/bin/tail -F /var/log/syslog, \