[V1][Metrics][Plugin] Add plugin support for custom StatLoggerBase implementations (#22456)

Signed-off-by: tovam <tovam@pliops.com>

tests/plugins/vllm_add_dummy_stat_logger/setup.py

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from setuptools import setup
+
+setup(
+    name="dummy_stat_logger",
+    version="0.1",
+    packages=["dummy_stat_logger"],
+    entry_points={
+        "vllm.stat_logger_plugins": [
+            "dummy_stat_logger = dummy_stat_logger.dummy_stat_logger:DummyStatLogger"  # noqa
+        ]
+    },
+)