Add FerryAPI as an OpenAI-compatible AI API gateway

[Sundry007]

Hi — suggesting FerryAPI as another OpenAI-compatible AI API gateway for the AI API proxy list.

Proposed entry:

• Website: https://www.ferryapi.io/
• Docs: https://www.ferryapi.io/docs
• Description: OpenAI-compatible AI API gateway for production apps, with prepaid usage-based billing, developer API key management, and lower-cost model access.

Why it fits:

• It matches the repo's focus on AI API proxy / OpenAI-compatible gateway services.
• It has public docs and a developer-facing setup flow.
• It is relevant for teams that need custom base_url, separate API keys, usage-based billing, and cost-sensitive model access.

Disclosure: I'm helping with FerryAPI growth, so please treat this as a transparent vendor suggestion. Happy to send a PR if you prefer.