pgsql: psql: Split extended query protocol meta-commands in --help=comm

psql: Split extended query protocol meta-commands in --help=commands

Compared to v17 with only \bind able to do extended query protocol work,
v18 has now a total of 11 meta-commands related to the extended query
protocol.  These were all listed under the "General" section of the
--help=commands output and are specialized, bloating the output
generated.

All these meta-commands are moved into a new section called "Extended
Query Protocol", listed at the end of --help=commands.

This split has been suggested by Noah Misch.

Discussion: https://postgr.es/m/20250415213450.1f.nmisch@google.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/78231baaf967166776de8262072acb8d589d3b6a

Modified Files
--------------
src/bin/psql/help.c | 29 ++++++++++++++++-------------
1 file changed, 16 insertions(+), 13 deletions(-)