nixos/jupyter: add env kernel option

nixos/modules/services/development/jupyter/kernel-options.nix

@@ -1,5 +1,5 @@
 # Options that can be used for creating a jupyter kernel.
-{lib }:
+{ lib }:
 
 with lib;
 
@@ -40,6 +40,15 @@ with lib;
       '';
     };
 
+    env = mkOption {
+      type = types.attrsOf types.str;
+      default = { };
+      example = { OMP_NUM_THREADS = "1"; };
+      description = lib.mdDoc ''
+        Environment variables to set for the kernel.
+      '';
+    };
+
     logo32 = mkOption {
       type = types.nullOr types.path;
       default = null;