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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