happa release v1.30.0

Update commands in the Get Started guide to use kubectl gs instead of gsctl by @kuosandys in https://github.com/giantswarm/happa/pull/2907
Improve app installation modal: keyboard accessibility and scrollable content by @kuosandys in https://github.com/giantswarm/happa/pull/2905
Fix flash messages duplication and content overflow by @kuosandys in https://github.com/giantswarm/happa/pull/2902
Prevent trying to use user information if the user gets logged out by @axbarsan in https://github.com/giantswarm/happa/pull/2906

Full Changelog: https://github.com/giantswarm/happa/compare/v1.29.0...v1.30.0