For uniformity with LTE where it already is.

We do not expose it in gnb schema because it will be exposed in both generic
LTE and NR schemas, but for ORS schemas I prefer to keep them intact myself.

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

Diff for rendered configs:

$ ./pythonwitheggs slapos-render-config.py && git diff -w --no-index config/{old,out}
diff --git a/config/old/gnb.cfg b/config/out/gnb.cfg
index 5849bb924..b8a385a71 100644
--- a/config/old/gnb.cfg
+++ b/config/out/gnb.cfg
@@ -56,6 +56,7 @@
     subcarrier_spacing: 30,
     ssb_pos_bitmap: "10000000",

+    root_sequence_index: 1,
     inactivity_timer: 10000,

       // Handover
@@ -176,7 +176,6 @@
     intra_freq_reselection: true,
     q_rx_lev_min: -70,
     q_qual_min: -20,
-    root_sequence_index: 1,
     sr_period: 40,
     dmrs_type_a_pos: 2,
     prach: {