installer: add ability to skip the default shell change
installer: add ability to skip the default shell change

Co-authored-by: Marshall Ford <08a5564a79b3d56562ff091aa4077e9abd0cdc3e@marshallford.me>
Co-authored-by: Joel Kuzmarski <49d054409f7d95b4e5aae7569cffe7dec0153cfa@gmail.com>

monological/oh-my-zsh,monological/oh-my-zsh,monological/oh-my-zsh,monological/oh-my-zsh