pgsql: auto_explain: Add new GUC, auto_explain.log_extension_options.

auto_explain: Add new GUC, auto_explain.log_extension_options.

The associated value should look like something that could be
part of an EXPLAIN options list, but restricted to EXPLAIN options
added by extensions.

For example, if pg_overexplain is loaded, you could set
auto_explain.log_extension_options = 'DEBUG, RANGE_TABLE'.
You can also specify arguments to these options in the same manner
as normal e.g. 'DEBUG 1, RANGE_TABLE false'.

Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com>
Reviewed-by: Lukas Fittl <lukas@fittl.com>
Discussion: http://postgr.es/m/CA+Tgmob-0W8306mvrJX5Urtqt1AAasu8pi4yLrZ1XfwZU-Uj1w@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/e972dff6c30447ebcfa2f8601b67f926247463b6

Modified Files
--------------
contrib/auto_explain/Makefile                      |   3 +-
contrib/auto_explain/auto_explain.c                | 387 +++++++++++++++++++++
.../auto_explain/expected/extension_options.out    |  49 +++
contrib/auto_explain/meson.build                   |   1 +
contrib/auto_explain/sql/extension_options.sql     |  33 ++
contrib/auto_explain/t/001_auto_explain.pl         |  18 +-
doc/src/sgml/auto-explain.sgml                     |  23 ++
src/tools/pgindent/typedefs.list                   |   2 +
8 files changed, 514 insertions(+), 2 deletions(-)