pgsql: Add COPY (on_error set_null) option

Add COPY (on_error set_null) option

If ON_ERROR SET_NULL is specified during COPY FROM, any data type
conversion errors will result in the affected column being set to a
null value.  A column's not-null constraints are still enforced, and
attempting to set a null value in such columns will raise a constraint
violation error.  This applies to a column whose data type is a domain
with a NOT NULL constraint.

Author: Jian He <jian.universality@gmail.com>
Author: Kirill Reshke <reshkekirill@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Jim Jones <jim.jones@uni-muenster.de>
Reviewed-by: "David G. Johnston" <david.g.johnston@gmail.com>
Reviewed-by: Yugo NAGATA <nagata@sraoss.co.jp>
Reviewed-by: torikoshia <torikoshia@oss.nttdata.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion:
https://www.postgresql.org/message-id/flat/CAKFQuwawy1e6YR4S%3Dj%2By7pXqg_Dw1WBVrgvf%3DBP3d1_aSfe_%2BQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2a525cc97e19868940c533787165bc7e7de3a80a

Modified Files
--------------
doc/src/sgml/monitoring.sgml             |  4 +-
doc/src/sgml/ref/copy.sgml               | 30 +++++++----
src/backend/commands/copy.c              |  7 ++-
src/backend/commands/copyfrom.c          | 54 +++++++++++++++-----
src/backend/commands/copyfromparse.c     | 88 +++++++++++++++++++++++++++-----
src/bin/psql/tab-complete.in.c           |  2 +-
src/include/commands/copy.h              |  1 +
src/include/commands/copyfrom_internal.h |  7 +++
src/test/regress/expected/copy2.out      | 58 +++++++++++++++++++++
src/test/regress/sql/copy2.sql           | 43 ++++++++++++++++
10 files changed, 253 insertions(+), 41 deletions(-)