[FEATURE] `Adapter.reshape()`

[jerrymhuang]

Feature Description
Very frequently, users have to change the shape of their simulation outputs as part of the configuration for generating the right data for training the approximator. Therefore, reshape() would be a great feature to have for the Adapter.

A (very rough) example usage is provided as below:

sim = {"x": np.arange(6)}

adapter = (
    bf.adapters.Adapter()
    # ...
    .reshape("x", to_shape=(3, 2))
    # ...
)