Add output_config to AnthropicChatGenerator ALLOWED_PARAMS

[ernoaapa]

Description

AnthropicChatGenerator.ALLOWED_PARAMS does not include output_config, which means it gets silently filtered out with a warning when passed via generation_kwargs.

The Anthropic API supports output_config as a top-level parameter (e.g., output_config: {"effort": "medium"}) to control adaptive thinking effort levels. This was introduced alongside adaptive thinking (thinking: {"type": "adaptive"}) for Claude Opus 4.6 and Sonnet 4.6.

Reference: https://platform.claude.com/docs/en/build-with-claude/adaptive-thinking#adaptive-thinking-with-the-effort-parameter

Current behavior

Passing output_config in generation_kwargs triggers a warning and the parameter is dropped:

Model parameters {'output_config'} are not allowed and will be ignored.

Expected behavior

output_config should be included in ALLOWED_PARAMS and passed through to the Anthropic SDK's messages.create(), similar to how thinking is already handled.

Suggested fix

Add "output_config" to the ALLOWED_PARAMS list in chat_generator.py.