pgsql: doc PG 19 relnotes: adjust pg_read_all_data & pg_write_all_data

doc PG 19 relnotes: adjust pg_read_all_data & pg_write_all_data

These were previously marked as functions, not roles, and were in the
wrong section.

Reported-by: 彭冲 <chong.peng@enmotech.com>

Discussion: /messages/by-id/tencent_5468291122A490C6578D9467@qq.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/3e744cc745b894b3712990b84729f805e4333147

Modified Files
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doc/src/sgml/release-19.sgml | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)