[Internal] Make runtime cloud trace also async (#3081)

# Description

Currently, the cloud trace in runtime is in sync mode. This seems
unnecessary. The local and runtime should use the same async pattern.

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- [ ] **The pull request does not introduce [breaking changes].**
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significant changes.**
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### Testing Guidelines
- [ ] Pull request includes test coverage for the included changes.

Co-authored-by: Yangtong Xu <[email protected]>

src/promptflow-devkit/promptflow/_sdk/_tracing.py

@@ -609,17 +609,11 @@ def process_otlp_trace_request(
                 else:
                     all_spans.append(span)
 
-    if cloud_trace_only:
-        # If we only trace to cloud, we should make sure the data writing is success before return.
-        _try_write_trace_to_cosmosdb(
-            all_spans, get_created_by_info_with_cache, logger, get_credential, is_cloud_trace=True
-        )
-    else:
-        # Create a new thread to write trace to cosmosdb to avoid blocking the main thread
-        ThreadWithContextVars(
-            target=_try_write_trace_to_cosmosdb,
-            args=(all_spans, get_created_by_info_with_cache, logger, get_credential, False),
-        ).start()
+    # Create a new thread to write trace to cosmosdb to avoid blocking the main thread
+    ThreadWithContextVars(
+        target=_try_write_trace_to_cosmosdb,
+        args=(all_spans, get_created_by_info_with_cache, logger, get_credential, cloud_trace_only),
+    ).start()
 
     return