[UCMConnector]Add has_connector_metadata (#6172)

### What this PR does / why we need it?
ucm_connector add has `has_connector_metadata` interface to adapt to the
latest KV connector in vLLM.

### Does this PR introduce _any_ user-facing change?
this PR doesn't introduce _any_ user-facing change.


### How was this patch tested?

- vLLM version: v0.14.0
- vLLM main:
d68209402d

Signed-off-by: UnifiedCacheManager <unifiedcachem@163.com>

vllm_ascend/distributed/kv_transfer/kv_pool/ucm_connector.py

@@ -43,6 +43,14 @@ class UCMConnectorV1(KVConnectorBase_V1):
     # ==============================
     # Worker-side methods
     # ==============================
+    def has_connector_metadata(self) -> bool:
+        """Check whether the connector metadata is currently set.
+
+        Returns:
+            bool: True if connector metadata exists, False otherwise.
+        """
+        return self._ucm_engine.has_connector_metadata()
+
     def register_kv_caches(self, kv_caches: dict[str, torch.Tensor]) -> None:
         """
         Initialize with the KV caches. Useful for pre-registering the