[FTS System test] Docs missing from Scorch index; upside_down intact

Build
6.0.0-1320

New System test (not merged yet)
./sequoia -scope tests/fts/scope_fts_component.yml -test tests/fts/test_fts_alice_component.yml -version 6.0.0-1320 -provider file:centos_second_cluster.yml

Steps
1. In a kv+fts (.206) single node cluster, create 2 buckets - default, other.
Start loading 10M docs to "other"
Start loading 10,492,816 to default bucket. Data ops/sec = 10-15k/sec on each bucket
2. Create scorch and upside_down index, of type default, both on bucket "other".
3. As data gets indexed, with the workload running in parallel, add 2 nodes- one with kv (.207) and another with kv+fts(.209). Start rebalance.
4. At the end of rebalance, compare index count of scorch vs upside_down index.

There are more phases in the system test but the run was aborted here.

Scorch index : 9996818 @ 99.97%
Upside down index: 10,000,000 @ 100%

as seen on UI. No fts activity seen from stats.

Also attaching screenshot of stats comparing indexes.

A couple of stat errors:

1. Both on upside down and scorch, the docs to persist is not 0.
2. No of docs remaining on scorch index is 0, while indexing progress says 99.97%.