Change config object name from gemini_provider.settings to ai_provider_gemini.settings

Usually the module name is used for its settings/config name ... so not sure about changing the config name ...
Maybe if this is something that it's expected by AI APIs.

However this MR brings nice update to use CONSTant for the settings ...
maybe we could have an interface .. GeminiProviderConfigInterface that could re-used in the module ...

just saying

I agree that it might be too late to change, but as it is still alpha, maybe it is time now or never. It is of course too late to change the module name :)
This issue purpose is a discussion first as it is not a requirement to follow AI module naming convention. So maybe this change is just "nice to have".

This is related to the module name.

When I started the module, there was no naming convention at all, even all the existing providers where part of the AI module. I agree its better if the module is renamed to ai_provider_gemini.

I am going to work on the renaming after we release this changes. After this I will see if its possible - we need to rename namespace in url/composer without affecting already installed instances. I will take care of this after this release, meanwhile I am setting this issue as postponed.