message: Add as code owner for GRM plugin
diff: /plugins/kafka-backend @backstage/reviewers @nirga
  /plugins/scaffolder-backend-module-yeoman @backstage/reviewers @pawelmitka
  /plugins/scaffolder-backend-module-rails @backstage/reviewers @angeliski
  +/plugins/git-release-manager @backstage/reviewers @erikengervall
  /tech-insights-backend @backstage/reviewers @xantier @iain-b
  /tech-insights-backend-module-jsonfc @backstage/reviewers @xantier @iain-b
  /tech-insights-tech-insights-common @backstage/reviewers @xantier @iain-b
  