Tutorial example for defining and importing faults and fractures with enhanced feature of `mesh_doctor`

[jhuang2601]

This PR:

• [x] Review the document to run mesh_doc to generate the mesh for T-shape frac
• [x] Prepare a python script to handle the mesh generation to assign global IDs
• [x] Instead of using InternalMesh, rerun the existing tutorial example with externally imported vtk mesh and check against the corresponding analytical solution
• [ ] Document the workflow and update the tutorial example