Add diagnostics support to Stookalert (#64747)

* Add diagnostics support to Stookalert

* coveragerc

.coveragerc

@@ -1069,6 +1069,7 @@ omit =
     homeassistant/components/stiebel_eltron/*
     homeassistant/components/stookalert/__init__.py
     homeassistant/components/stookalert/binary_sensor.py
+    homeassistant/components/stookalert/diagnostics.py
     homeassistant/components/stream/*
     homeassistant/components/streamlabswater/*
     homeassistant/components/suez_water/*

homeassistant/components/stookalert/diagnostics.py

@@ -0,0 +1,19 @@
+"""Diagnostics support for Stookalert."""
+from __future__ import annotations
+
+from typing import Any
+
+import stookalert
+
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.core import HomeAssistant
+
+from .const import DOMAIN
+
+
+async def async_get_config_entry_diagnostics(
+    hass: HomeAssistant, entry: ConfigEntry
+) -> dict[str, Any]:
+    """Return diagnostics for a config entry."""
+    client: stookalert.stookalert = hass.data[DOMAIN][entry.entry_id]
+    return {"state": client.state}