Move step running into enum for dynamic ordering (#1188)

Co-authored-by: Stuart Reilly <sreilly@scottlogic.com>

src/steps/os/macos.rs

@@ -1,8 +1,9 @@
 use crate::command::CommandExt;
 use crate::execution_context::ExecutionContext;
+use crate::step::Step;
 use crate::terminal::{print_separator, prompt_yesno};
+use crate::utils::require;
 use crate::utils::{get_require_sudo_string, require_option};
-use crate::{utils::require, Step};
 use color_eyre::eyre::Result;
 use rust_i18n::t;
 use std::collections::HashSet;