Pass full aman into preprocess pipe

[mmccrackan]

Addresses #1323.

Replacement for #1346 since the preprocessing infrastructure changed and the code could be simplified. This allows passing in an unrestricted preprocessing axis manager into the pipeline run function so that the total number of detectors is preserved when running the multiple layers as opposed to the current implementation where the second layer only retains the number of detectors left after the first layer cuts.

Tested by running preproc_or_load_group with both layers and checking the dimensions of proc_aman prior to saving. Also tested with multilayer_load_and_preprocess and confirmed both calls to get_meta return the full dimensions.