pgsql: Add target "slru" to pg_stat_reset_shared()

Add target "slru" to pg_stat_reset_shared()

Currently, pg_stat_reset_shared() cannot reset the counters in the view
pg_stat_slru even if it is a type of shared stats.  This patch adds
support for a new value in pg_stat_reset_shared(), called "slru", able
to do that.  Note that pg_stat_reset_shared(NULL) also resets SLRU
counters.

There may be a point in removing pg_stat_reset_slru() that was
introduced in 28cac71bd368 (v13~) as the new option overlaps with this
function, but we would lose the ability to reset individual SLRU
counters.  This is left for future reconsideration.

Author: Atsushi Torikoshi
Discussion: https://postgr.es/m/e3c25d72e81378e7b64f3c52e0306fc9@oss.nttdata.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/2e8a0edc2a3321582d5da65690b0371654c7a44f

Modified Files
--------------
doc/src/sgml/monitoring.sgml        |  6 ++++++
src/backend/utils/adt/pgstatfuncs.c |  5 ++++-
src/test/regress/expected/stats.out | 23 ++++++++++++++++++++++-
src/test/regress/sql/stats.sql      |  7 +++++++
4 files changed, 39 insertions(+), 2 deletions(-)