ENH: add STC PVC to PETPVC interface

[mnoergaard]

Summary

This PR adds single-target PVC correction to the PETPVC interface in Nipype. The STC is already included in PETPVC, however, the interface needs to be updated to reflect these changes.

Fixes #3633

List of changes proposed in this PR (pull-request)

1. Add the 'STC' option to the 'pvc' flag in the PETPVC interface

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.15%. Comparing base (bedb5b4) to head (2592106).

Additional details and impacted files

@@ Coverage Diff @@ ## master #3634 +/- ## ======================================= Coverage 63.15% 63.15% ======================================= Files 308 308 Lines 40825 40825 Branches 5656 5656 ======================================= Hits 25781 25781 Misses 14031 14031 Partials 1013 1013 

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