doc: Release notes refinements
In particular, make some more precise links for some major items.
Branch
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REL_12_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/3e3e32a1c160ec4e2342068515dfaf1dd04c6078
Modified Files
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doc/src/sgml/ref/alter_table.sgml | 2 +-
doc/src/sgml/release-12.sgml | 23 ++++++++++++-----------
2 files changed, 13 insertions(+), 12 deletions(-)