pgsql: doc: Explain that ANALYZE ignores reject_limit in file_fdw

doc: Explain that ANALYZE ignores reject_limit in file_fdw

The documentation did not explain that ANALYZE on file_fdw foreign tables
ignores reject_limit, which could lead users to expect it to fail when
the number of skipped rows exceeded the limit.

Ignoring the limit allows statistics to be collected from valid rows
even when the limit is exceeded. These statistics can still be useful for
queries using LIMIT, for example, which may finish before encountering
enough conversion errors to exceed reject_limit.

Document this exception and its rationale.

Backpatch to v18, where reject_limit support was added to file_fdw.

Author: Ayoub Kazar <ayoub(dot)kazar(at)data-bene(dot)io>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/6cc479df-7571-4393-a572-f46dba1bfcbf@data-bene.io
Backpatch-through: 18

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/cb88c3204a3b94832dea72be99815a4a26251a3c

Modified Files
--------------
contrib/file_fdw/file_fdw.c | 6 +++++-
doc/src/sgml/file-fdw.sgml | 5 ++++-
2 files changed, 9 insertions(+), 2 deletions(-)