Add SpatialReference Information to Outputs

[bendhouseart]

Error from validator:

Derivative: /derivatives/petprep/
        [ERROR] SIDECAR_KEY_REQUIRED A data file's JSON sidecar is missing a key listed as required.
                SpatialReference
                /desc-aparcaseg_dseg.tsv - Field description: String or object describing the reference image to which the current image is aligned.
For images with a single reference, the value MUST be a single string.
For images with multiple references, such as surface and volume references,
a JSON object MUST be used. - rules.sidecars.derivatives.atlas.TemplateNonStandard

Examples of files affected:

• *_dseg.tsv
• *_desc-brain_mask.json
• *_desc-hmc_petref.json
• /sub-01/ses-baseline/pet/sub-01_ses-baseline_space-MNI152NLin2009cAsym_desc-preproc_pet.json
• /sub-01/ses-baseline/pet/sub-01_ses-baseline_space-MNI152NLin2009cAsym_petref.json

[bendhouseart]

Fixed some of these that were false positives via this update to the spec.

Still, I think it would be worth while to define which of the source images is being used as the reference space during pipeline execution.