Update NVFlare FL spleen seg example to use MONAIClientAlgo

[holgerroth]

Is your feature request related to a problem? Please describe. This example needs updating to use new MONAIAlgo and bundle configuration (once ready) https://github.com/Project-MONAI/tutorials/tree/main/federated_learning/nvflare/nvflare_spleen_example

Describe the solution you'd like Update example to use MONAIAlgo and bundle configs, see https://github.com/Project-MONAI/MONAI/issues/4612. It will also need integration with NVFlare (adding a ClientAlgoExecutor)

Describe alternatives you've considered n/a

Additional context n/a