Specify ssh-keys as list of strings, rather than having a single string.

Older versions of nixpkgs allowed you to specify multiple keys by having newline separated keys in your string. However, this worked essentially by accident, and is now explictly disallowed.

I noticed this because I had configured multiple keys for the local grid. This isn't currently impacting my ability to work, but it seems like a worthwhile improvement anyway. This will be necessary (for example) if/when multiple people are given root access to our storage nodes.

CC: @jcalderone, @florian This will require updating morph/grid/local/public-keys/users.nix locally if/when this lands.

morph/grid/local/public-keys/users.nix.example

+let
 # Add your public key. Example:
-# let key = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHx7wJQNqKn8jOC4AxySRL2UxidNp7uIK9ad3pMb1ifF flo@fs-la";
+# key = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHx7wJQNqKn8jOC4AxySRL2UxidNp7uIK9ad3pMb1ifF flo@fs-la";
 # You can use the following to get key from the local machine.
-# let key = builtins.readFile ~/.ssh/id_ed25519.pub;
-let key = undefined;
-in { "root" = key; "vagrant" = key; }
+# key = builtins.readFile ~/.ssh/id_ed25519.pub;
+  key = undefined;
+  keys = [key]
+in {
+  "root" = keys;
+  "vagrant" = keys;
+}