pgsql: doc PG relnotes: add links to commits

doc PG relnotes: add links to commits

Discussion: /messages/by-id/ZuYsS5XdA7hVcV9l@momjian.us

Backpatch-through: 12

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/5fd150379bbecce2a5e3798f2fce7c796eb00f73

Modified Files
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doc/src/sgml/release-15.sgml | 741 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 741 insertions(+)