GreatCell benchmark suite, Hydraulic fracturing, HM_PHASE_FIELD

This merge request adds Phase 4 of the GreatCell benchmark suite (DECOVALEX-2027). It includes a new Jupyter notebook demonstrating hydraulic fracturing using OGS’s HM_PHASE_FIELD process. Phases 1 (see !5297 (merged), merged) and 2 (!5370 (merged)) covered the LIE approach. Phase 3 involved mechanical and hydro-mechanical deformation of intact and statically fractured samples using HM_PHASE_FIELD—see !5373 (merged).