backstage release v2.21.0

Added

• (repositories) The Create form describes create → scaffold → pull request as the person, offers Generate CircleCI config (gen.ci.generate) with the refusal’s fix as one click, and its dry run carries the reason in #2433 by @teemow

Full Changelog: https://github.com/giantswarm/backstage/compare/v2.20.1...v2.21.0