Add base docker image

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

overlays/default.nix

@@ -1,4 +1,5 @@
-final: prev: {
+final: prev:
+{
   lib = prev.lib.recursiveUpdate prev.lib {
     fetchers = {
       sshKnownHosts = import ./fetchers/sshKnownHosts final prev;
@@ -11,3 +12,9 @@ final: prev: {
     };
   };
 }
+// (import ../packages { pkgs = final; })
+// {
+  dockerImages = prev.dockerImages or { } // {
+    base = final.docker-image-base;
+  };
+}