Feature Request: Support custom request body parameters (extra_body) for API providers #1104

Is your feature request related to a problem? Please describe.
Certain API providers (such as Fireworks AI, OpenRouter, and others) support or require vendor-specific parameters inside the JSON request body. For example, Fireworks AI supports "store": false to enforce per-request Zero Data Retention (ZDR), as detailed in their official documentation:
https://docs.fireworks.ai/guides/security_compliance/data_handling

Currently, there is no option in ZooCode's provider settings to pass custom payload properties into outgoing API requests.

Describe the solution you'd like
Add a configuration field (e.g., "Extra Body" or "Custom Payload Parameters" as a JSON input). This field should inject user-defined key-value pairs directly into the JSON request body sent to the API, similar to how extra_body works in LiteLLM or OpenAI's Python/TS SDKs.

Describe alternatives you've considered
Currently, the only workaround is running a local proxy server like LiteLLM to intercept ZooCode's outgoing requests, inject "store": false into the payload, and forward the request to the provider.

Additional context

• Fireworks AI Data Handling Reference: https://docs.fireworks.ai/guides/security_compliance/data_handling
• Adding native support for custom body parameters would significantly improve privacy management (e.g., disabling data storage on providers) and flexibility with emerging LLM features without requiring users to maintain a local proxy infrastructure.