UX: add confirmation dialog for user archive export

app/assets/javascripts/discourse/controllers/user.js.es6

@@ -69,7 +69,16 @@ export default ObjectController.extend(CanCheckEmails, {
     },
 
     exportUserArchive: function() {
-      Discourse.ExportCsv.exportUserArchive();
+      bootbox.confirm(
+        I18n.t("admin.export_csv.user_archive_confirm"),
+        I18n.t("no_value"),
+        I18n.t("yes_value"),
+        function(confirmed) {
+          if (confirmed) {
+            Discourse.ExportCsv.exportUserArchive();
+          }
+        }
+      );
     }
   }
 });

config/locales/client.en.yml

@@ -1729,6 +1729,7 @@ en:
             confirm: "Are your sure you want to rollback the database to the previous working state?"
 
       export_csv:
+        user_archive_confirm: "Are you sure you want to download your posts?"
         success: "Export initiated, you will be notified via private message when the process is complete."
         failed: "Export failed. Please check the logs."
         rate_limit_error: "Posts can be downloaded once per day, please try again tomorrow."