Add support for AdapterPlus

[julian-fong]

This PR aims to add support for AdapterPlus

Github: https://github.com/visinf/adapter_plus Paper: https://arxiv.org/pdf/2406.06820

Integration of AdapterPlus into the adapters library will involve adding new parameters/options to the BnConfig

Checklist of things that are added/to be added

1. New type of scaling called channel, in which we add learnable parameters for the channel/input_size dimension
2. New type of init_weights called houlsby, where the projection matrices $W_{down}$ and $W_{up}$ will be initialized with zero-centered Gaussian with a standard deviation of $10^{-2}$ truncated at 2 standard deviations, and zeros for bias
3. Support for drop_path, also known as stochastic depth ONLY applicable for vision based tasks