ants: output transforms naming (ants_registration_sy_n)

[kaitj]

The output of ants_registration_sy_n currently returns the provided prefix with an asterisk (e.g. {ants_prefix}*).

>> print(b0_to_t1.output_transform)

sub-XX_ses-YY_run-1_*

Is it possible to return a tuple/list of ouput paths based on the transformation type? I think the suffixes are known but this would also avoid new users from having to know the file names beforehand to replace the asterisk in downstream "nodes".

May also affect other ants commands