Add gtm tracking for GitLab export project imports

app/views/projects/_import_project_pane.html.haml

@@ -8,7 +8,7 @@
     .import-buttons
       - if gitlab_project_import_enabled?
         .import_gitlab_project.has-tooltip{ data: { container: 'body', qa_selector: 'gitlab_import_button' } }
-          = link_to new_import_gitlab_project_path, class: 'gl-button btn-default btn btn_import_gitlab_project js-import-project-btn', **tracking_attrs(track_label, 'click_button', 'gitlab_export') do
+          = link_to new_import_gitlab_project_path, class: 'gl-button btn-default btn btn_import_gitlab_project js-import-project-btn', data: { platform: 'gitlab_export', **tracking_attrs_data(track_label, 'click_button', 'gitlab_export') } do
             .gl-button-icon
               = sprite_icon('tanuki')
             = _("GitLab export")