pgsql: Add support for --extension in pg_dump

Add support for --extension in pg_dump

When specified, only extensions matching the given pattern are included
in dumps. Similarly to --table and --schema, when --strict-names is
used, a perfect match is required. Also, like the two other options,
this new option offers no guarantee that dependent objects have been
dumped, so a restore may fail on a clean database.

Tests are added in test_pg_dump/, checking after a set of positive and
negative cases, with or without an extension's contents added to the
dump generated.

Author: Guillaume Lelarge
Reviewed-by: David Fetter, Tom Lane, Michael Paquier, Asif Rehman,
Julien Rouhaud
Discussion: https://postgr.es/m/CAECtzeXOt4cnMU5+XMZzxBPJ_wu76pNy6HZKPRBL-j7yj1E4+g@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6568cef26e0f40c25ae54b8e20aad8d1410a854b

Modified Files
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doc/src/sgml/ref/pg_dump.sgml | 43 +++++++++++--
src/bin/pg_dump/pg_dump.c | 93 +++++++++++++++++++++++++++--
src/test/modules/test_pg_dump/t/001_base.pl | 53 ++++++++++------
3 files changed, 161 insertions(+), 28 deletions(-)