Add disk usage endpoint to supervisor (#2750)

Author: MindFreeze

docs/api/supervisor/endpoints.md

@@ -1906,6 +1906,68 @@ Shutdown the host
 
 </ApiEndpoint>
 
+<ApiEndpoint path="/host/disks/<disk>/usage" method="get">
+Get detailed disk usage information in bytes.
+
+The only supported `disk` for now is "default". It will return usage info for the data disk.
+
+Supports an optional `max_depth` query param. Defaults to 1
+
+**Example response:**
+
+```json
+{
+  "id": "root",
+  "label": "Default",
+  "total_space": 503312781312,
+  "used_space": 430245011456,
+  "children": [
+    {
+      "id": "system",
+      "label": "System",
+      "used_space": 75660903137
+    },
+    {
+      "id": "addons_data",
+      "label": "Addons data",
+      "used_space": 42349200762
+    },
+    {
+      "id": "addons_config",
+      "label": "Addons configuration",
+      "used_space": 5283318814
+    },
+    {
+      "id": "media",
+      "label": "Media",
+      "used_space": 476680019
+    },
+    {
+      "id": "share",
+      "label": "Share",
+      "used_space": 37477206419
+    },
+    {
+      "id": "backup",
+      "label": "Backup",
+      "used_space": 268350699520
+    },
+    {
+      "id": "ssl",
+      "label": "SSL",
+      "used_space": 202912633
+    },
+    {
+      "id": "homeassistant",
+      "label": "Home assistant",
+      "used_space": 444090152
+    }
+  ]
+}
+```
+
+</ApiEndpoint>
+
 ### Ingress
 
 <ApiEndpoint path="/ingress/panels" method="get">