muster release v5.43.1

Helm: MusterMCPServerFailed stays silent for a sibling installation that is down. A hub reaches a sibling’s servers as <mc>-mcp-<type>; when every one of them, two at least, is Failed, the sibling counts as down, its own heartbeat is the alert, and its servers no longer fire one alert each on every hub. A sibling server failing while another of the sibling’s servers is not Failed still fires, and so do a single-server sibling, the installation’s own <installation>-mcp-<type> servers and every server outside the naming. The promtool suite covers the three cases. (giantswarm/agent-platform#1066)