add: load function for AccelerateRLModel

[dongs0104]

save and load are being done in different ways.

After performing the example, the model that was save at ckpts
it call

trlx/trlx/model/accelerate_base_model.py

Line 139 in 1a3461d

def save(self, directory=None):

when I use ckpts weight it call

trlx/trlx/model/__init__.py

Line 119 in 1a3461d

def load(self, fp: str, title: str = "OUT"):

[jon-tow]

Good catch and thanks for the fix! I've left a nit and change request.

[jon-tow]

Thanks again @dongs0104 !