[Feature Request] Expose `strict_json_schema` argument in `activity(nexus)_as_tool` in OpenAI SDK integration

[antlai-temporal]

Currently, the OpenAI SDK integration hardwires strict_json_schema=True in https://github.com/temporalio/sdk-python/blob/main/temporalio/contrib/openai_agents/workflow.py#L152 and L238 .

The current workaround is to use dataclasses.replace on the result, but it could be cleaner to pass it as an argument to activity_as_tool, as suggested by a Temporal customer...

[tconley1428]

Seems reasonable and easy. We'll put it in the pipeline.