feat(utils): freeze module

[FateScript]

close #1105 , I add UT for adjust_status also.

Simple example code for users who want to freeze backbone.

class Exp(MyExp):
    ...
    def get_model(self):
        from yolox.utils import freeze_module
        model = super().get_model()
        freeze_module(model.backbone.backbone)
        # freeze_module(model.backbone)  # freeze FPN also
        return model

Plz review kindly. @GOATmessi7 @Joker316701882

[GOATmessi8]

LGTM.