agent-platform release v4.12.0

Added

• (meta) The stateful singletons can be pinned to on-demand capacity (scheduling.singletons, opt-in); muster-valkey takes the #431 guards (#439) in #442 by @teemow

Full Changelog: https://github.com/giantswarm/agent-platform/compare/v4.11.0...v4.12.0