Organise ~/milestones code

...avascripts/filtered_search/available_dropdown_mappings.js

app/assets/javascripts/milestones/form.js

app/assets/javascripts/milestones/index.js

app/assets/javascripts/milestones/init_milestones_show.js

app/assets/javascripts/milestones/milestone_select.js

...ts/javascripts/milestones/promote_milestone_modal_init.js

app/assets/javascripts/milestones/utils.js

app/assets/javascripts/pages/groups/milestones/edit/index.js

app/assets/javascripts/pages/groups/milestones/new/index.js

app/assets/javascripts/pages/groups/milestones/show/index.js

...ssets/javascripts/pages/projects/milestones/edit/index.js

...sets/javascripts/pages/projects/milestones/index/index.js

...assets/javascripts/pages/projects/milestones/new/index.js

...ssets/javascripts/pages/projects/milestones/show/index.js

...components/filtered_search_bar/tokens/milestone_token.vue

...avascripts/filtered_search/available_dropdown_mappings.js

...frontend/milestones/components/milestone_combobox_spec.js

spec/frontend/milestones/utils_spec.js

...onents/filtered_search_bar/tokens/milestone_token_spec.js