Merged PR 3117982: Add fanout network and shell creds definition

After Github PR sonic-net#1742 is merged, we need to explicitly define the fanout credentials for accessing fanout network cli and Linux shell.

Author: wangxin

ansible/group_vars/fanout/secrets.yml

@@ -6,9 +6,9 @@ fanout_sonic_user: admin
 fanout_sonic_password: password
 
 # Credential for accessing the network cli interface
-fanout_network_user: netadmin
-fanout_network_password: netpassword
+fanout_network_user: admin
+fanout_network_password: "{{ secret_group_vars['str']['lab_admin_pass']}}"
 
 # Credential for accessing the Linux shell
-fanout_shell_user: shelladmin
-fanout_shell_password: shellpassword
+fanout_shell_user: "{{ secret_group_vars['str']['fanout_admin_user']}}"
+fanout_shell_password: "{{ secret_group_vars['str']['fanout_admin_password']}}"