Endpoint URL for `api.openai.com` hardcoded

[petski]

See https://platform.openai.com/docs/guides/your-data#how-to-use-data-residency, and I quote:

For US processing, the URL is https://us.api.openai.com/. For EU processing, the URL is https://eu.api.openai.com/

Currently, the api.openai.com domain is hardcoded at least in:

src/platform/src/Bridge/OpenAi/Whisper/ModelClient.php:        return new RawHttpResult($this->httpClient->request('POST', \sprintf('https://api.openai.com/v1/audio/%s', $endpoint), [
src/platform/src/Bridge/OpenAi/Embeddings/ModelClient.php:        return new RawHttpResult($this->httpClient->request('POST', 'https://api.openai.com/v1/embeddings', [
src/platform/src/Bridge/OpenAi/DallE/ModelClient.php:        return new RawHttpResult($this->httpClient->request('POST', 'https://api.openai.com/v1/images/generations', [
src/platform/src/Bridge/OpenAi/Gpt/ModelClient.php:        return new RawHttpResult($this->httpClient->request('POST', 'https://api.openai.com/v1/chat/completions', [

A couple of PlatformResponseFactory's already seem to work with a baseUrl strategy. I'd like to propose the 4 ModelClient's above implement something simular.

[OskarStark]

@chr-hertel what's your take on this? For this special case, we might add sth via the options like region=US or region=EU. Open it for a base url could lead to someone "misusing" this for other providers, which just adapt the OpenAI API spec and I don't know if we want that.

[chr-hertel]

I like the region idea, yes 👍

[OskarStark]

#409 in the making

[OskarStark]

@petski does #409 works for you?

[petski]

Love it! Thanks @OskarStark! I left some remarks in the PR.