[Plugin] Make plugin group clear (#26757)

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

vllm/plugins/__init__.py

@@ -9,7 +9,14 @@ import vllm.envs as envs
 
 logger = logging.getLogger(__name__)
 
+# Default plugins group will be loaded in all processes(process0, engine core
+# process and worker processes)
 DEFAULT_PLUGINS_GROUP = "vllm.general_plugins"
+# IO processor plugins group will be loaded in process0 only
+IO_PROCESSOR_PLUGINS_GROUP = "vllm.io_processor_plugins"
+# Platform plugins group will be loaded in all processes when
+# `vllm.platforms.current_platform` is called and the value not initialized,
+PLATFORM_PLUGINS_GROUP = "vllm.platform_plugins"
 
 # make sure one process only loads plugins once
 plugins_loaded = False