backstage release v2.88.0-rc.1

Added

• (scaffolder-backend-module-gs,gs-node) Gs:oci:tagExists scaffolder action in #2717 by @marians

Changed

• (e2e) Agentlab specs pass or skip on a default lab in #2716 by @teemow

Full Changelog: https://github.com/giantswarm/backstage/compare/v2.87.0...v2.88.0-rc.1