Add instrumentation for `Moderations.create()`

The OpenAI integration does not instrument the Moderations API endpoint.

**Endpoint to instrument:**

* `openai.resources.Moderations.create()` (sync + async)

**Attributes to capture:**

* Model name
* Input text (if `send_default_pii` and `include_prompts` are enabled)
* Flagged status and categories from the response
* Category scores (if useful for telemetry)
* Follow OTel GenAI semantic conventions for span naming and attributes

**Reference:** [OpenAI integration compliance review](<../openai-integration-compliance-review.md>), Section 6