ref(explore): exclude internal expand param from OpenAPI spec

The expand=context param is internal-only (gated behind
data-browsing-attribute-context), so hide it from the public spec while
keeping it functional.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: DominikB2014

src/sentry/api/endpoints/organization_trace_item_attributes.py

@@ -194,6 +194,9 @@ def get_result(self, limit, cursor=None):
     many=True,
     type=str,
     enum=["context"],
+    # Internal-only for now: gated behind the data-browsing-attribute-context
+    # feature, so exclude it from the public OpenAPI spec.
+    exclude=True,
     description=(
         "Optional fields to expand. Pass `context` to include the sentry "
         "conventions metadata (brief, examples, deprecation, etc.) for "