[REQUEST] Softmax activation function for encoders

[Tengoles]

Is there a particular reason why softmax activation functions are not supported? I undertand they can be useful for a resource allocation scenario. As far as I can tell, adding it only requires a slight change in this file:

d3rlpy/d3rlpy/models/utility.py

Line 8 in 5ab2b46

def create_activation(activation_type: str) -> nn.Module:

[takuseno]

@Tengoles Hi, thanks for the issue. I feel that softmax is not a common choice for an activation function. Do you have any papers where softmax activation is actually used?