As with Radio Units and cells organize a registry of peer cells and start to handle
that registry generally everywhere. The registry is still populated with only
LTE cells on enb and only NR cells on gnb, but the only place that is aware of
that is registry loading routine.

In the old code defaults were noticed for tac to be 1 if not provided, and so
those defaults are pushed to live in ORS now. ORS schemas are also updated
because that defaults were not declared there.

Generic switches to use peer/cell/lte directly which means that now it accepts
e_cell_id instead of cell_id as the name for full E-UTRAN cell identity. Full
backward compatibility is provided for ORS which implements translation of its
original schema to the new generic one.

Tests will be added later as full tests for generic MultiRU.

Rendered enb.cfg and gnb.cfg change a bit, but the changes are mostly due to
reordering of fields. The only change with semantic value is

    -          ssb_nr_arfcn: ,
    +          ssb_nr_arfcn: 520090,

in gnb.cfg .

The old configuration was invalid anyway because if it is only

              ssb_nr_arfcn: ,

then enb does not start with the following error:

    # ../lteenb gnb.cfg
    gnb.cfg:119: unexpected token: ','

Like with many other handover-related fields
https://tech-academy.amarisoft.com/lteenb.doc#prop.ncell_list.ssb_nr_arfcn
documents that ssb_nr_arfcn "Must be present" for Inter-gNB HO case. The old
code was erroneously doing `ncell.get(name, '')` with yielding empty string in
case a parameter is missing, which is corrected here.

--------

Appendix. Diff for rendered enb.cfg and gnb.cfg before and after this patch:

```
$ ./pythonwitheggs slapos-render-config.py && xdiff -w config/{old,out}
```

```diff
diff --git a/config/old/enb.cfg b/config/out/enb.cfg
index 1a2c41b6b..252c2e379 100644
--- a/config/old/enb.cfg
+++ b/config/out/enb.cfg
@@ -46,9 +46,9 @@
         // Inter-ENB HO
         {
           rat:          "eutra",
+          cell_id:      0x12345,  // -> 1
           n_id_cell:    35,
           dl_earfcn:    700,
-          cell_id:      0x12345,
           tac:          123,
         },
       ],
diff --git a/config/old/gnb.cfg b/config/out/gnb.cfg
index 635c4baf2..b401f3513 100644
--- a/config/old/gnb.cfg
+++ b/config/out/gnb.cfg
@@ -58,14 +58,14 @@
         // Inter-ENB HO
         {
           rat:          "nr",
+          nr_cell_id:   0x77712, // -> 1
+          gnb_id_bits:  22,
+          n_id_cell:    75,
           dl_nr_arfcn:  520000,
-          ssb_nr_arfcn: ,
+          band:         38,
+          ssb_nr_arfcn: 520090,
           ul_nr_arfcn:  520000,
-          n_id_cell:    75,
-          gnb_id_bits:  22,
-          nr_cell_id:   0x77712,
           tac:          321,
-          band:         38,
           ssb_subcarrier_spacing: 30,
           ssb_period: 20,
           ssb_offset: 0,
```