spaceapid: adjustments to 3d printer state sensors

- Prefix sensor names with ext_ as the spec says we should use that for
  extensions (this also improves attribute access for tools that don't
  like fields starting with a number)
- Rename printer state to printer busy state, to make it clearer.
- Add ext_3d_printer_minutes_remaining sensors

config/hosts/public-web-static/spaceapid-config/ccchh-dynamic.json

@@ -25,13 +25,13 @@
           ]
         }
       ],
-      "3d_printer_state": [
+      "ext_3d_printer_busy_state": [
         {
           "sensor_data": {
             "unit": "bool",
             "location": "Loetschlauch",
             "name": "mk4",
-            "description": "Prusa mk4 state"
+            "description": "Prusa mk4 busy state"
           },
           "allowed_credentials": [
             "club-assistant"
@@ -42,7 +42,31 @@
             "unit": "bool",
             "location": "Loetschlauch",
             "name": "mk3.5",
-            "description": "Prusa mk3.5 state"
+            "description": "Prusa mk3.5 busy state"
+          },
+          "allowed_credentials": [
+            "club-assistant"
+          ]
+        }
+      ],
+      "ext_3d_printer_minutes_remaining": [
+        {
+          "sensor_data": {
+            "unit": "minutes_remaining",
+            "location": "Loetschlauch",
+            "name": "mk4",
+            "description": "Prusa mk4 minutes remaining"
+          },
+          "allowed_credentials": [
+            "club-assistant"
+          ]
+        },
+        {
+          "sensor_data": {
+            "unit": "minutes_remaining",
+            "location": "Loetschlauch",
+            "name": "mk3.5",
+            "description": "Prusa mk3.5 minutes remaining"
           },
           "allowed_credentials": [
             "club-assistant"