pgsql: doc: \123 and \x12 escapes in COPY are in database encoding.

doc: \123 and \x12 escapes in COPY are in database encoding.

The backslash sequences, including \123 and \x12 escapes, are interpreted
after encoding conversion. The docs failed to mention that.

Backpatch to all supported versions.

Reported-by: Andreas Grob
Discussion: https://www.postgresql.org/message-id/17142-9181542ca1df75ab%40postgresql.org

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f90c05959ec3fb712cba889817e0a0689fa6fa89

Modified Files
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doc/src/sgml/ref/copy.sgml | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)