In other words merge enb and gnb into sole enb that can handle both LTE and NR
cells at the same time and simultaneously.

Previously which type of Radio Access Technology to use - LTE or NR - was
static parameter of particular software - it was possible to instantiate cells
only with selected RAT for particular template.

In MultiRU it is possible to generally instantiate all kind of cells -
LTE/NR and TDD/FDD all at the same time and each served by a different kind of Radio Unit.

-> Switch cell type to be runtime parameter as the final step to be able to do that.

For generic cell definitions are now required to come with cell_type=lte|nr
parameter. In schemas cell_list now includes oneOf for lte|nr cell instead of
particular cell type. Similar adaption is done for ncell_list and
x2_peers/xn_peers are merged into just peers with similar oneOf.

Global gnb-specific parameters of went-away gnb are also added as global ones to enb:

  - gnb_id
  - gnb_id_bits
  - amf_list
  - plmn_list (as plmn_list_5g not to conflict with plmn_list)
  - nssai

They must be present if there are NR cells.

Full backward compatibility is preserved for ORS: now it injects cells to
generic with particular cell_type annotations and translates ORS-specific
x2_peers/xn_peers and gnb/plmn_list to proper generic parameters.

In ORS-gnb schema gnb_stats_fetch_period and gnb_drb_stats_enabled had to be
renamed to enb_stats_fetch_period and enb_drb_stats_enabled, but once again,
full backward compatibility is preserved because ORS mode already had the
following in its proxy:

    {#- backward compatibility: if ORS is running in gnb mode, and gnb_* parameters
        are present, replace their generic enb_* counterparts with gnb_* ones #}
    ...

The diff for rendered enb.cfg and gnb.cfg, that simulate ORS, before and after
hereby patch is also empty.