agent-platform release v4.7.18

Fixed

• (substrate) Pin the platform Harness’s image in atelet’s image cache — atelet.imageCache.pinnedImages derived from kagent.harness.image; the Substrate line re-pins to v0.0.27-gs.6 in #405 by @teemow

Full Changelog: https://github.com/giantswarm/agent-platform/compare/v4.7.17...v4.7.18