feat(agent): report btrfs filesystems as storage pools (#2315)

Co-authored-by: henrygd <hank@henrygd.me>

internal/alerts/alerts.go

@@ -66,6 +66,7 @@ type SystemAlertGPUData struct {
 }
 
 type SystemAlertZfsPool struct {
+	Raw   bool    `json:"raw,omitempty"`
 	Total float64 `json:"d"`
 	Used  float64 `json:"du"`
 }