pgsql: relnotes: add null logical replication item

relnotes: add null logical replication item

Also move system view item to logical replication, mention "infinite
_error_ loops".

Reported-by: Euler Taveira, Takamichi Osumi, Amit Langote

Discussion: /messages/by-id/21e8ef3b-6ffb-49d8-867f-4622a4dffcf3@www.fastmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/3715850ecc524544546e696bb0a7bbc44095d12a

Modified Files
--------------
doc/src/sgml/release-15.sgml | 44 +++++++++++++++++++++++++++-----------------
1 file changed, 27 insertions(+), 17 deletions(-)