pgsql: Document limit on the number of out-of-line values per table

Document limit on the number of out-of-line values per table

Document the hard limit stemming from the size of an OID, and also
mention the perfomance impact that occurs before the hard limit
is reached.

Jakub Wartak and Robert Haas
Backpatch to all supported versions

Discussion: https://postgr.es/m/CAKZiRmwWhp2yxjqJLwbBjHdfbJBcUmmKMNAZyBjjtpgM9AMatQ%40mail.gmail.com

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e51160fa0bab7203e37094fbb0349b0c324b09e7

Modified Files
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doc/src/sgml/limits.sgml | 11 +++++++++++
1 file changed, 11 insertions(+)