Tighten neighbour-cell config parsing by enforcing parameter constraints in
the descriptor and switching parsing code to name-based lookups with gpd.
Changes:
- Update `GNBNEIGHBOURCELLPARAMS_DESC` in `openair2/GNB_APP/gnb_paramdef.h`
to add checks for `physical id`, `absoluteFrequencySSB`, `scs`, `band`
`tracking_area_code`.
- Remove neighbour-cell parameter index macros.
- Refactor `parse_neighbour_cells_list` in `openair2/GNB_APP/gnb_config.c`
to use `gpd()` lookups for neighbour fields instead of fixed indexes.
- Extend `parse_neighbour_cells_list` with an `n_cell_params` argument and
update `fill_neighbour_cell_configuration` to pass
`sizeofArray(ncell_params)`.