backstage release v3.15.0

Added

• (agent-platform) Workspace picker in the new-session composer by @teemow — Starting a session offers a workspace next to the agent, remembered per agent (Last used with <agent>). The portal first checks that you can read all of its repositories and names those you can’t, with Start without workspace. Shown only where the installation has a workspace-manager and you have a workspace.

Full Changelog: https://github.com/giantswarm/backstage/compare/v3.14.2...v3.15.0