Hi Gourami,
The command itself is "all user" ; but you don't have to add every single user by itself, unless you don't want to grant all of them access to the VPN ( I think you can also manage this from the AD without reverting back to the SRX ).
I think this is the statement you are referring to ( bold ):
Under security > dynamic-vpn,add all the users that are going to use the dynamic VPN. The command is as follows:
set security dynamic-vpn clients all user