oh-my-zsh: add module (#25140)

* programs.zsh: add enableOhMyZsh option to automate setup of oh-my-zsh in global zshrc

* programs.zsh: make oh-my-zsh plugins configurable

* programs.zsh: add ohMyZshCustom option

* programs.zsh: add ohMyZshTheme option

* programs.zsh: applying minor fixes to evaluate expressions properly

* programs.zsh: fix ordering of oh-my-zsh config and execution

* programs.zsh: move all oh-my-zsh params into its own scope named programs.zsh.oh-my-zsh

nixos/modules/programs/zsh/zsh.nix

@@ -99,6 +99,7 @@ in
         '';
       };
 
+
     };
 
   };
@@ -143,7 +144,6 @@ in
 
         ${cfge.interactiveShellInit}
 
-
         HELPDIR="${pkgs.zsh}/share/zsh/$ZSH_VERSION/help"
       '';