pgsql: Docs: consolidate dependency notes in pg_dump and pg_restore

Docs: consolidate dependency notes in pg_dump and pg_restore

The pg_dump documentation had repetitive notes for the --schema,
--table, and --extension switches, noting that dependent database
objects are not automatically included in the dump. This commit removes
these notes and replaces them with a consolidated paragraph in the
"Notes" section.

pg_restore had a similar note for -t but lacked one for -n; do likewise.

Also, add a note to --extension in pg_dump to note that ancillary files
(such as shared libraries and control files) are not included in the
dump and must be present on the destination system.

Author: Florents Tselai <florents(dot)tselai(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/284C4D55-4F90-4AA0-84C8-1E6A28DDF271@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/78bf28e3bf504db0eea5e3bcb3c43e9908108480

Modified Files
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doc/src/sgml/ref/pg_dump.sgml | 41 +++++++++++++++-------------------------
doc/src/sgml/ref/pg_restore.sgml | 20 ++++++++++----------
2 files changed, 25 insertions(+), 36 deletions(-)