Add diagnostics platform for GIOS integration (#69918)

* Add diagnostics platform

* Fix fixture data

homeassistant/components/gios/diagnostics.py

@@ -0,0 +1,24 @@
+"""Diagnostics support for GIOS."""
+from __future__ import annotations
+
+from dataclasses import asdict
+
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.core import HomeAssistant
+
+from . import GiosDataUpdateCoordinator
+from .const import DOMAIN
+
+
+async def async_get_config_entry_diagnostics(
+    hass: HomeAssistant, config_entry: ConfigEntry
+) -> dict:
+    """Return diagnostics for a config entry."""
+    coordinator: GiosDataUpdateCoordinator = hass.data[DOMAIN][config_entry.entry_id]
+
+    diagnostics_data = {
+        "config_entry": config_entry.as_dict(),
+        "coordinator_data": asdict(coordinator.data),
+    }
+
+    return diagnostics_data