pgsql: Report NULL as total backup size if it's not estimated.

Report NULL as total backup size if it's not estimated.

Previously 0 was reported in pg_stat_progress_basebackup.total_backup
if the total backup size was not estimated. Per discussion, our consensus
is that NULL is better choise as the value in total_backup in that case.
So this commit makes pg_stat_progress_basebackup view report NULL
in total_backup column if the estimation is disabled.

Bump catversion.

Author: Fujii Masao
Reviewed-by: Amit Langote, Magnus Hagander, Alvaro Herrera
Discussion: https://postgr.es/m/CABUevExnhOD89zBDuPvfAAh243RzNpwCPEWNLtMYpKHMB8gbAQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/67e0adfb3f98f1e4a89a32b6f2e59774ce579146

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 2 +-
doc/src/sgml/ref/pg_basebackup.sgml | 2 +-
src/backend/catalog/system_views.sql | 2 +-
src/backend/replication/basebackup.c | 19 +++++++++++++++++--
src/include/catalog/catversion.h | 2 +-
src/test/regress/expected/rules.out | 5 ++++-
6 files changed, 25 insertions(+), 7 deletions(-)