Use a constant to reference homeassistant domain (#113889)

* Use CONF_CORE to reference `homeassistant` domain

* Just use DOMAIN

* USE DOMAIN for `homeasistant` domain in config_schema.py

* Use DOMAIN_HA as constant for homeassistant domain

* Rename CONF_CORE to DOMAIN_HA

* Rename DOMAIN_HA to HA_DOMAIN

* Use relative import

* Use direct imports

script/hassfest/config_schema.py

@@ -4,13 +4,15 @@ from __future__ import annotations
 
 import ast
 
+from homeassistant.core import DOMAIN as HA_DOMAIN
+
 from .model import Config, Integration
 
 CONFIG_SCHEMA_IGNORE = {
     # Configuration under the homeassistant key is a special case, it's handled by
     # conf_util.async_process_ha_core_config already during bootstrapping, not by
     # a schema in the homeassistant integration.
-    "homeassistant",
+    HA_DOMAIN,
 }