Migrate solax away from using async_add_job (#113257)

The plan is to deprecate `async_add_job` to reduce the number of job APIs we have to maintain.

See #113179 for additional history.

`async_add_job` was not being used as expected here

homeassistant/components/solax/sensor.py

@@ -103,8 +103,12 @@ async def async_setup_entry(
     serial = resp.serial_number
     version = resp.version
     endpoint = RealTimeDataEndpoint(hass, api)
-    hass.async_add_job(endpoint.async_refresh)
-    async_track_time_interval(hass, endpoint.async_refresh, SCAN_INTERVAL)
+    entry.async_create_background_task(
+        hass, endpoint.async_refresh(), f"solax {entry.title} initial refresh"
+    )
+    entry.async_on_unload(
+        async_track_time_interval(hass, endpoint.async_refresh, SCAN_INTERVAL)
+    )
     devices = []
     for sensor, (idx, measurement) in api.inverter.sensor_map().items():
         description = SENSOR_DESCRIPTIONS[(measurement.unit, measurement.is_monotonic)]