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