feat(baselines) Add FedDefender Baseline

[gautamjajoo]

Description

Add baseline FedDefender to flower-baseline.
Reproduce experiments on MNIST.

Related issues/PRs

Fixes #4565

Checklist

• Implement proposed change
• Write tests
• Update documentation
• Make CI checks pass
• Ping maintainers on Slack (channel #contributions)

[jafermarq]

Hi @gautamjajoo , great to see a PR for FedDefender !! I took a quick first look at your code but I noticed the structure of the baseline doesn't follow the new format for baselines (see the steps for contributing new baselines changed a couple of months ago: https://flower.ai/docs/baselines/how-to-contribute-baselines.html

Now you can create a new baseline by executing:

flwr new feddefender --framework="Flower Baseline"

and then make the relevant edits to the code that gets auto-generated. For the most part you'll just need to move the code in this PR around a bit, remove the Hydra config system and make small edits in the README.md (see that the readme in the generated baseline project also details how to complete the process).

Please ping me if you have some questions. Happy to help. In the meantime i'll revert the status of this PR to Draft. Feel free to update it to "ready for Review" once you want us to take a first look at it.