[Frontend][4/N] Improve all pooling task | Add plugin pooling task (#26973)

Signed-off-by: wang.yuqi <noooop@126.com>
Signed-off-by: Christian Pinto <christian.pinto@ibm.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Christian Pinto <christian.pinto@ibm.com>

vllm/pooling_params.py

@@ -84,6 +84,11 @@ class PoolingParams(
             msg = f"You cannot overwrite {self.task=!r} with {task=!r}!"
             raise ValueError(msg)
 
+        # plugin task uses io_processor.parse_request to verify inputs,
+        # skipping PoolingParams verify
+        if self.task == "plugin":
+            return
+
         # NOTE: Task validation needs to done against the model instance,
         # which is not available in model config. So, it's not included
         # in this method