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_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/c9aa6f4f86fc244f56d4fcdf2ee0154bb3ecac84

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