Enable autocomplete features on iteration forms

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/349517

Changelog: added
EE: true

app/views/layouts/_init_auto_complete.html.haml

 - object = @target_project || @project || @group
-- noteable_type = @noteable.class if @noteable.present?
+- noteable_type = @noteable_type || @noteable&.class
 
 - datasources = autocomplete_data_sources(object, noteable_type)
 

ee/app/assets/javascripts/iterations/components/iteration_form_without_vue_router.vue

@@ -46,7 +46,7 @@ export default {
       iterations: [],
       loading: false,
       title: this.iteration.title,
-      description: this.iteration.description,
+      description: this.iteration.description ?? '',
       startDate: this.iteration.startDate,
       dueDate: this.iteration.dueDate,
     };

ee/app/controllers/groups/iterations_controller.rb

@@ -4,6 +4,7 @@ class Groups::IterationsController < Groups::ApplicationController
   before_action :check_iterations_available!
   before_action :authorize_show_iteration!, only: [:index, :show]
   before_action :authorize_create_iteration!, only: [:new, :edit]
+  before_action :set_noteable_type, only: [:show, :new, :edit]
 
   feature_category :team_planning
 
@@ -17,6 +18,10 @@ class Groups::IterationsController < Groups::ApplicationController
 
   private
 
+  def set_noteable_type
+    @noteable_type = Iteration
+  end
+
   def check_iterations_available!
     render_404 unless group.licensed_feature_available?(:iterations)
   end

ee/app/views/groups/iterations/edit.html.haml

+- @gfm_form = true
 - add_to_breadcrumbs _("Iterations"), group_iterations_path(@group)
 - breadcrumb_title params[:id]
 - page_title s_("Iterations|Edit iteration")

ee/app/views/groups/iterations/new.html.haml

+- @gfm_form = true
 - add_to_breadcrumbs _("Iterations"), group_iterations_path(@group)
 - breadcrumb_title _("New")
 - page_title _("Iterations")

ee/app/views/groups/iterations/show.html.haml

+- @gfm_form = true
 - add_to_breadcrumbs _("Iterations"), group_iterations_path(@group)
 - breadcrumb_title params[:id]
 - page_title _("Iterations")