pgsql: doc: Clarify units for io_combine_limit and io_max_combine_limit

doc: Clarify units for io_combine_limit and io_max_combine_limit.

If these parameters are set without units, the values are interpreted
as blocks. This detail was previously missing from the documentation,
so this commit adds it.

Backpatch to v17 where io_combine_limit was added.

Author: Karina Litskevich <litskevichkarina(at)gmail(dot)com>
Reviewed-by: Chao Li <lic(at)highgo(dot)com>
Reviewed-by: Xuneng Zhou <xunengzhou(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CACiT8iZCDkz1bNYQNQyvGhXWJExSnJULRTYT894u4-Ti7Yh6jw@mail.gmail.com
Backpatch-through: 17

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d83da466b59bd4523806a084b39cda90dc9c11e4

Modified Files
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doc/src/sgml/config.sgml | 4 ++++
1 file changed, 4 insertions(+)