Add Progressbar to Milestone Page (#25050)

This is adds the progress bar, which is already on the Milestone List,
also to the Page of a Single Milestone.


![grafik](https://github.com/go-gitea/gitea/assets/15185051/24e0fa28-369b-4bb9-807a-ee823b46ba81)

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Co-authored-by: silverwind <me@silverwind.io>

options/locale/locale_en-US.ini

@@ -1759,7 +1759,7 @@ milestones.no_due_date = No due date
 milestones.open = Open
 milestones.close = Close
 milestones.new_subheader = Milestones organize issues and track progress.
-milestones.completeness = %d%% Completed
+milestones.completeness = <strong>%d%%</strong> Completed
 milestones.create = Create Milestone
 milestones.title = Title
 milestones.desc = Description