pgsql: Update PQparameterStatus and ParameterStatus docs

Update PQparameterStatus and ParameterStatus docs

Cover scram_iterations, which was added in commit b577743000cd.  While
at it, turn the list into a <simplelist> with 2 columns, which is much
nicer to read.

In master, remove mentions of antediluvian versions before which some
parameters were not reported.

Noticed while investigating a question by Maiquel Grassi.

Backpatch to 16.

Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/202401301236.mc5ebrohhtsd@alvherre.pgsql

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/17f3196599303abbfc605f5ea5c5e314ce856e38

Modified Files
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doc/src/sgml/libpq.sgml    | 34 +++++++++++++++++++---------------
doc/src/sgml/protocol.sgml | 34 +++++++++++++++++++---------------
2 files changed, 38 insertions(+), 30 deletions(-)