Adding some CL subnetworking strategies (WSN and RMN)

[niniack]

Hi,

We typically have a roadmap issue pinned but I didn't see that, so I'm just starting the conversation here.

I was hoping to contribute two subnetworking strategies (Winning Subnetworks and Relevance Mapping Networks). I think I have implementations that are architecture agnostic, unlike the ones published by the original authors.

If someone from the core team can just give me a thumbs up that here is interest in this, then I'd like to open up a PR soon! While I have a close to merge-able implementation, I imagine I will still have to do some cleaning up, more testing, and a bit of back and forth in design decisions!

WSN: https://arxiv.org/abs/2303.14962
RMN: https://arxiv.org/abs/2102.11343