Add diagnostics to GDACS integration (#125296)

* simple diagnostics

* add service status information

* remove from no diagnostics list

* wip

* cater for the case where status info is undefined

* make test work

* code reformatted

* add snapshot data

* simplify code

script/hassfest/manifest.py

@@ -117,7 +117,6 @@ NO_IOT_CLASS = [
 # https://github.com/home-assistant/developers.home-assistant/pull/1512
 NO_DIAGNOSTICS = [
     "dlna_dms",
-    "gdacs",
     "geonetnz_quakes",
     "hyperion",
     "nightscout",