Add custom_preprocessing_pipeline option

[alejoe91]

Adds the option of passing a custom_preprocessing_pipeline as parameter.

If used, all the steps (excluding motion correction) are controlled by the custom pipeline.

See SpikeInterface docs for reference:

• https://spikeinterface.readthedocs.io/en/latest/api.html#spikeinterface.preprocessing.apply_preprocessing_pipeline
• https://spikeinterface.readthedocs.io/en/latest/how_to/build_pipeline_with_dicts.html