provider: add Gonka Broker

[iamoeco]

Description: (required)

• Add Gonka Broker as a new provider. Gonka Broker is an OpenAI-compatible inference API, so the integration reuses the open-ai-base chat/completion params and response transformers, mirroring the existing lambda provider.
• New src/providers/gonkabroker/api.ts sets the base URL https://proxy.gonkabroker.com/v1, a Authorization: Bearer header, and /chat/completions + /completions endpoint mapping.
• New src/providers/gonkabroker/index.ts wires chatComplete and complete via open-ai-base. No default model is baked in: the provider is a pure pass-through, so the inherited open-ai-base default (gpt-3.5-turbo) is cleared with { model: undefined }. An omitted model then returns a clean error from the upstream API instead of silently routing to a model the provider does not serve. Model identity belongs to the caller.
• Register the provider: GONKABROKER const + VALID_PROVIDERS entry in src/globals.ts, and the import + provider-map entry in src/providers/index.ts.

Tests Run/Test cases added: (required)

• Verified against a locally running gateway (npm run dev:node) with a real API key. POST /v1/chat/completions with x-portkey-provider: gonkabroker returned HTTP 200 with a valid OpenAI-shaped completion ("provider":"gonkabroker").
• Verified a request without model returns an error from the provider rather than routing to a default model, confirming the pass-through behavior.
• npm run format:check passes; npm run build succeeds.

Type of Change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

[iamoeco]

Hi @VisargD @narengogi — gentle bump 🙏 The only pending check is the first-contributor CI gate awaiting a maintainer's "approve and run". The PR mirrors the existing lambda provider (4 files, pure pass-through, mergeable). Could you approve the run and take a look? Thanks!