Allow init_asl_t1_trans_wf to accept flexible set of native-space inputs to warp

[tsalo]

Summary

The main difference between ASLPrep's init_asl_t1_trans_wf and fMRIPrep's init_bold_t1_trans_wf is the list of native-space files to warp to T1w space. ASLPrep has ASL versions of many of the same files (ref_bold_brain, ref_bold_mask, t1w_brain, t1w_mask, t1w_aseg, t1w_aparc, bold_split), but it also has a bunch of CBF outputs to warp as well.

If the workflow could ingest multiple native-space inputs without having to specify them in the function, then ASLPrep could directly use fMRIPrep's function (perhaps moved to niworkflows?).

[tsalo]

One additional difference is that init_asl_t1_trans_wf calls the ASL reference workflow, which in turn uses aslcontext.

[tsalo]

I have a plan: I will call the BOLD versions, but ignore the reference image output. Then I will call the ASL-specific reference workflow in the main workflow instead.