Add API key management endpoints for LLM proxies and providers in gateway controller

Description

In standalone gateway mode (without platform-api), API key management is only supported for regular APIs via /apis/{id}/api-keys endpoints. LLM proxies and LLM providers do not have equivalent API key endpoints in the gateway controller REST API.

When using the platform-api, API keys work for all three resource types (APIs, LLM proxies, LLM providers) because the platform-api generates keys and pushes them to gateways via WebSocket events. However, in standalone mode this functionality is missing for LLM resources.

The underlying apikeyxds infrastructure in the gateway controller is already resource-agnostic (keys are stored by UUID), so the core mechanism already supports this.

What needs to be done:

• Add POST /llm-proxies/{id}/api-keys — Create API key for an LLM proxy
• Add GET /llm-proxies/{id}/api-keys — List API keys for an LLM proxy
• Add PUT /llm-proxies/{id}/api-keys/{apiKeyName} — Update API key for an LLM proxy
• Add POST /llm-proxies/{id}/api-keys/{apiKeyName}/regenerate — Regenerate API key for an LLM proxy
• Add DELETE /llm-proxies/{id}/api-keys/{apiKeyName} — Revoke API key for an LLM proxy
• Add equivalent endpoints for /llm-providers/{id}/api-keys
• Update api/openapi.yaml with the new endpoints
• Regenerate server code via oapi-codegen

Version

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Related Issue

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