fzf: add enableZshIntegration option

When enabled this will extend user's `$HOME/.zshrc` with sourcing of fzf's
completion and key-bindings integration libraries.

(cherry picked from commit f8398339a3)

modules/programs/fzf.nix

@@ -55,6 +55,14 @@ in
         Whether to enable Bash integration.
       '';
     };
+
+    enableZshIntegration = mkOption {
+      default = true;
+      type = types.bool;
+      description = ''
+        Whether to enable Zsh integration.
+      '';
+    };
   };
 
   config = mkIf cfg.enable {
@@ -74,5 +82,10 @@ in
       . ${pkgs.fzf}/share/fzf/completion.bash
       . ${pkgs.fzf}/share/fzf/key-bindings.bash
     '';
+
+    programs.zsh.initExtra = mkIf cfg.enableZshIntegration ''
+      . ${pkgs.fzf}/share/fzf/completion.zsh
+      . ${pkgs.fzf}/share/fzf/key-bindings.zsh
+    '';
   };
 }