[Feature]: Add an option in the agent to specify the architecture of the DQN agent

[yonatank93]

Motivation

Currently, the architecture of the model is hard-coded. However, this might be too restrictive: maybe sometimes we need smaller model if we only care about building an agent for specific ECMs, or maybe we want larger model for more generalized ECMs.

Proposed solution

I think it is straightforward enough to implement this. I actually have a working draft already.

Alternatives considered

Not applied