I have managed to set up my server with a default user 'admin'. The sshKeys in the metadata is set with the following format, described in the google documentation.
key: sshKeys value: admin:ssh-rsa XXXXXXXXXX
However, I am trying to add a new user to the system, hence I updated the metadata to the following
key: sshKeys value: admin:ssh-rsa XXXXXXXXXX newuser:ssh-rsa YYYYYYYYY
This has worked perfectly for me on one instance of server that I have set up sometime back. However I was unable to set it up on the new one. Can someone help me out with this?