[2.0] Stop setting option flow config_entry explicitly

[strawgate]

Detected that custom integration 'elasticsearch' sets option flow config_entry explicitly, which is deprecated at custom_components/elasticsearch/config_flow.py, line 373: self.config_entry = config_entry. This will stop working in Home Assistant 2025.12, please create a bug report at https://github.com/legrego/homeassistant-elasticsearch/issues

[strawgate]

Will require 2024.11: https://github.com/home-assistant/developers.home-assistant/pull/2435/files

The config entry is apparently already available under self.handler and the entry id is available under self._config_entry_id