Move /etc/group generation to the installer

This ensures that the gid's for the auto-generated user groups stay in
sync with the gid in /etc/passwd. It also makes it easier to evolve the
format of /etc/group in the future.

config/base.toml

@@ -105,15 +105,6 @@ path = "/dev/stderr"
 data = "libc:stderr"
 symlink = true
 
-# Group settings
-[[files]]
-path = "/etc/group"
-data = """
-root;0;root
-user;1000;user
-sudo;1;user
-"""
-
 # User settings
 [users.root]
 password = "password"
@@ -125,3 +116,8 @@ home = "/root"
 [users.user]
 # Password is unset
 password = ""
+
+# Group settings
+[groups.sudo]
+gid = 1
+members = ["user"]