Autodownload and test meshes

[suvarchal]

implements automated mesh download and testing pipeline for different meshes (e.g, https://swiftbrowser.dkrz.de/objects/FESOM_MESHES2.1/) , enabling automatic retrieval, partitioning, and validation of meshes by generating mesh diags, we could eventually test full simulation for at least few time steps.

here are meshes generated for meshes listed in mesh mesh_registry.json in tests directory

 tree -P *diag.nc
.
├── CMakeFiles
├── remote_generate_meshdiag_core2_mpi16
│   └── results
│       └── fesom.mesh.diag.nc
├── remote_generate_meshdiag_dars_mpi128
│   └── results
│       └── fesom.mesh.diag.nc
├── remote_generate_meshdiag_ng5_mpi512
│   └── results
│       └── fesom.mesh.diag.nc
├── remote_generate_meshdiag_orca25_mpi128
│   └── results
│       └── fesom.mesh.diag.nc
└── remote_generate_meshdiag_pi_remote_mpi8
   └── results
       └── fesom.mesh.diag.nc

this PR also restructures ctests, groups them cleanly and adds mesh partitioner and mesh diag tests.