Fix CSV issues import max file size message

By default, maxAttachmentSize is undefined which does not show up
properly in user interface

Changelog: fixed

app/views/projects/issues/_nav_btns.html.haml

@@ -9,7 +9,7 @@
   - if show_feed_buttons
     = render 'shared/issuable/feed_buttons'
 
-  .js-csv-import-export-buttons{ data: { show_export_button: show_export_button.to_s, show_import_button: show_import_button.to_s, issuable_type: issuable_type, issuable_count: issuables_count_for_state(issuable_type.to_sym, params[:state]), email: notification_email, export_csv_path: export_csv_project_issues_path(@project, request.query_parameters), import_csv_issues_path: import_csv_namespace_project_issues_path, container_class: 'gl-mr-3', can_edit: can_edit.to_s, project_import_jira_path: project_import_jira_path(@project) } }
+  .js-csv-import-export-buttons{ data: { show_export_button: show_export_button.to_s, show_import_button: show_import_button.to_s, issuable_type: issuable_type, issuable_count: issuables_count_for_state(issuable_type.to_sym, params[:state]), email: notification_email, export_csv_path: export_csv_project_issues_path(@project, request.query_parameters), import_csv_issues_path: import_csv_namespace_project_issues_path, container_class: 'gl-mr-3', can_edit: can_edit.to_s, project_import_jira_path: project_import_jira_path(@project), max_attachment_size: number_to_human_size(Gitlab::CurrentSettings.max_attachment_size.megabytes) } }
 
   - if @can_bulk_update
     = button_tag _("Edit issues"), class: "gl-button btn btn-default gl-mr-3 js-bulk-update-toggle"