pgsql: Track statistics for streaming of changes from ReorderBuffer.

Track statistics for streaming of changes from ReorderBuffer.

This adds the statistics about transactions streamed to the decoding
output plugin from ReorderBuffer. Users can query the
pg_stat_replication_slots view to check these stats and call
pg_stat_reset_replication_slot to reset the stats of a particular slot.
Users can pass NULL in pg_stat_reset_replication_slot to reset stats of
all the slots.

Commit 9868167500 has added the basic infrastructure to capture the stats
of slot and this commit extends the statistics collector to track
additional information about slots.

Bump the catversion as we have added new columns in the catalog entry.

Author: Ajin Cherian and Amit Kapila
Reviewed-by: Sawada Masahiko and Dilip Kumar
Discussion: https://postgr.es/m/CAA4eK1+chpEomLzgSoky-D31qev19AmECNiEAietPQUGEFhtVA@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/8e90ec5580d5345fef31005d7cc2215ba2125070

Modified Files
--------------
doc/src/sgml/monitoring.sgml                    | 38 +++++++++++++++++++++++++
src/backend/catalog/system_views.sql            |  3 ++
src/backend/postmaster/pgstat.c                 | 11 ++++++-
src/backend/replication/logical/logical.c       | 19 +++++++++----
src/backend/replication/logical/reorderbuffer.c | 20 +++++++++++++
src/backend/replication/slot.c                  |  2 +-
src/backend/utils/adt/pgstatfuncs.c             |  9 ++++--
src/include/catalog/catversion.h                |  2 +-
src/include/catalog/pg_proc.dat                 |  6 ++--
src/include/pgstat.h                            |  8 +++++-
src/include/replication/reorderbuffer.h         |  5 ++++
src/test/regress/expected/rules.out             |  5 +++-
12 files changed, 111 insertions(+), 17 deletions(-)