openai-v2: import OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT from genai-utils

Remove local re-definition of OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT
and import it from opentelemetry.util.genai.environment_variables instead,
making genai-utils the single source of truth for this constant.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: nagkumar91

instrumentation-genai/opentelemetry-instrumentation-openai-v2/src/opentelemetry/instrumentation/openai_v2/utils.py

@@ -36,6 +36,9 @@
     error_attributes as ErrorAttributes,
 )
 from opentelemetry.trace.status import Status, StatusCode
+from opentelemetry.util.genai.environment_variables import (
+    OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT,
+)
 from opentelemetry.util.genai.types import (
     InputMessage,
     LLMInvocation,
@@ -45,10 +48,6 @@
     ToolCallResponse,
 )
 
-OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT = (
-    "OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT"
-)
-
 
 def is_content_enabled() -> bool:
     capture_content = environ.get(