pgsql: doc: document the need to analyze partitioned tables

doc: document the need to analyze partitioned tables

Autovacuum does not do it.

Reported-by: Justin Pryzby

Discussion: /messages/by-id/20210913035409.GA10647@telsasoft.com

Backpatch-through: 11

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/c576acc7078d3f4eb8bfda199a05d794a28eb82c

Modified Files
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doc/src/sgml/maintenance.sgml | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)