`sagemaker_config` related `Networking` bugs in `ModelTrainer`

[admivsn]

PySDK Version

• PySDK V2 (2.x)
• [x ] PySDK V3 (3.x)

Describe the bug
2 closely related Networking bugs in ModelTrainer that prevent the use of sagemaker_config.

1. Incorrect parameter used here in Networking definition causing Pydantic ValidationError:

                self.networking = Networking(
                    default_enable_network_isolation=default_enable_network_isolation,

2. Networking security_group_ids not successfully added here in a silent bug.

            if self.networking.subnets is None:
                self.networking.subnets = self.config_mgr.resolve_value_from_config(
                    config_path=TRAINING_JOB_SUBNETS_PATH
                )
            if self.networking.security_group_ids is None:
                self.networking.subnets = self.config_mgr.resolve_value_from_config( 
                    config_path=TRAINING_JOB_SUBNETS_PATH
                )

To reproduce

from sagemaker.core.helper.session_helper import Session
from sagemaker.train.model_trainer import ModelTrainer

sagemaker_config = {
    "SageMaker": {
        "TrainingJob": {
            "VpcConfig": {
                "SecurityGroupIds": ["sg-blah"],
                "Subnets": ["subnet-blah"]
            }
        }
    },
    "SchemaVersion": "1.0",
}

sagemaker_session = Session(sagemaker_config=sagemaker_config)

model_trainer = ModelTrainer(
    training_image="685385470294.dkr.ecr.eu-west-1.amazonaws.com/sagemaker-xgboost:1.7-1",
    sagemaker_session=sagemaker_session,
)

# Error occurs here when SDK tries to instantiate Networking 
model_trainer.train(input_data_config={})

ValidationError: 1 validation error for Networking
default_enable_network_isolation
  Extra inputs are not permitted [type=extra_forbidden, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.13/v/extra_forbidden

Expected behavior
sagemaker_config variables to be successfully added to ModelTrainer.