[skip ci] adding PluginSettings

ml-agents/mlagents/trainers/cli_utils.py

         "--plugins",
         default="",
         type=str,
-        nargs=3,
+        nargs="*",
         help="Absolute paths of plugins to be loaded",
         required=False
     )

ml-agents/mlagents/trainers/learn.py

 import sys
 import importlib
 import pkgutil
+from mlagents.trainers.initializer import Initializer
-
-
-class Initializer:
-    def __init__(self):
-        pass
-
-    def load(self):
-        pass
 
 
 def get_all_subclasses(cls):
 
     for p in paths:
         sys.path.append(p)
+    print(sys.path)
 
     discovered_plugins = {
         name: importlib.import_module(name)

ml-agents/mlagents/trainers/settings.py

 
 
 @attr.s(auto_attribs=True)
+class PluginSettings:
+    plugins: Optional[List[str]] = parser.get_default("plugins")
+
+
+@attr.s(auto_attribs=True)
 class RunOptions(ExportableSettings):
     behaviors: DefaultDict[str, TrainerSettings] = attr.ib(
         factory=lambda: collections.defaultdict(TrainerSettings)
     environment_parameters: Optional[Dict[str, EnvironmentParameterSettings]] = None
     checkpoint_settings: CheckpointSettings = attr.ib(factory=CheckpointSettings)
+    plugin_settings: PluginSettings = attr.ib(factory=PluginSettings)
-    plugins: List[str] = parser.get_default("plugins")
+    cattr.register_structure_hook(PluginSettings, strict_to_cls)
     cattr.register_structure_hook(EngineSettings, strict_to_cls)
     cattr.register_structure_hook(CheckpointSettings, strict_to_cls)
     cattr.register_structure_hook(