Creation of distributed LS skeleton

[laetitia-m]

1. Creation of the distributed LS skeleton:
   • Add the LS skeleton in a new file ls_pmmg.c
   • Add the LS step into the function PMMG_preprocessMesh_distributed in libparmmg.c file
   • Wrap PMMG_parmmglib_distributed into a generalized PMMG_parmmg_distributed function
2. Modify verbosity option in analysis_pmmg.c
3. Fix minor bugs in ci tests for pvtu output
4. Fix a typo in src/libparmmg_tools.c: change filname into filename