ENH: Convert SlicerTractParcellation s4ext to json file

Also update category from "Libraries" to "Diffusion"

Author: jcfr

SlicerTractParcellation.json

@@ -0,0 +1,8 @@
+{
+  "$schema": "https://raw.githubusercontent.com/Slicer/Slicer/main/Schemas/slicer-extension-catalog-entry-schema-v1.0.0.json#",
+  "build_dependencies": [],
+  "build_subdirectory": "inner-build",
+  "category": "Diffusion",
+  "scm_revision": "main",
+  "scm_url": "https://github.com/SlicerDMRI/SlicerTractParcellation"
+}