Create Google Generative AI Conversation integration (#93156)

* Copy openai_conversation to google_generative_ai_conversation
This is to improve diff of the next commit with the actual implementation.

Commands used:
cp -r homeassistant/components/openai_conversation/ homeassistant/components/google_generative_ai_conversation/
cp -r tests/components/openai_conversation/ tests/components/google_generative_ai_conversation/

find homeassistant/components/google_generative_ai_conversation/ tests/components/google_generative_ai_conversation/ -type f | xargs sed -i \
-e 's@openai_conversation@google_generative_ai_conversation@g' \
-e 's@OpenAI Conversation@Google Generative AI Conversation@g' \
-e 's@balloob@tronikos@g'

* Add google_generative_ai_conversation to Google brand

* Google Generative AI Conversation

* Sync recent openai changes

* handle empty responses