feat: finish the host-metrics plugin, move host status into core (B16)

drizzle/sqlite/0041_nosy_mystique.sql

@@ -0,0 +1,6 @@
+-- ssh_data.stats_config split: its status half moved to status_check_enabled
+-- and status_check_interval, its metrics half to the host-metrics plugin's
+-- host settings. Both copies run at boot, after this migration, so a real
+-- DROP COLUMN here would delete the data first. The column stays in place,
+-- unused, until 3.0.0.
+SELECT 1;