Create SlicerBrats.json

I have created one extension and have added all the scripted CLI extensions. 
SlicerBratsPreprocessor
SlicerBratsSegmentator
SlicerBratsFusionator
Also I have added the scripted module
BatchBrainMRTumorSegmentation which is calling the above cli modules to perform preprocessing, segmentation and lastly fusion.

Author: saimasafdar2021

SlicerBrats.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": ".",
+  "category": "SlicerBrats",
+  "scm_revision": "main",
+  "scm_url": "https://github.com/UWA-Medical-Physics/SlicerBrats.git"
+}