Hardware status admin api (#218)

* Add metrics for disk usage

* Add admin API for hardware metrics

* Fix error message alert

controllers/admin/hardware.go

@@ -0,0 +1,16 @@
+package admin
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/gabek/owncast/metrics"
+)
+
+// GetHardwareStats will return hardware utilization over time
+func GetHardwareStats(w http.ResponseWriter, r *http.Request) {
+	metrics := metrics.Metrics
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(metrics)
+}