Add petref-mni_registration json with ANTs details to perform PET to MNI normalization

### What would you like to see added in this software?

As a part of the development of PETQC, it is required to add a PET-specific ANTs json file to allow for adequate registration between native PET to MNI. 

### Do you have any interest in helping implement the feature?

Yes

### Additional information / screenshots

_No response_