pgsql: Fix and improve several places in the docs

Fix and improve several places in the docs

This adds some missing markups, fixes a couple of incorrect ones and
clarifies some documentation in various places.

Author: Liudmila Mantrova
Discussion: https://postgr.es/m/a068f947-7a51-5df1-b3fd-1a131ae5c044@postgrespro.ru
Backpatch-through: 12

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/de14e54d7bd71f9256aae08dec832af25da3fd35

Modified Files
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doc/src/sgml/backup.sgml                  | 14 +++++++-------
doc/src/sgml/biblio.sgml                  |  9 +++------
doc/src/sgml/ref/alter_foreign_table.sgml |  4 ++--
doc/src/sgml/ref/pg_checksums.sgml        |  2 +-
doc/src/sgml/ref/pg_dump.sgml             |  2 +-
doc/src/sgml/ref/pg_rewind.sgml           |  2 +-
doc/src/sgml/ref/pgbench.sgml             |  8 ++++----
doc/src/sgml/ref/reindex.sgml             | 14 +++++++-------
8 files changed, 26 insertions(+), 29 deletions(-)