Add GUC variable to print original query to the server logs when there

doc/src/sgml/runtime.sgml

src/backend/utils/error/elog.c

src/backend/utils/misc/guc.c

src/backend/utils/misc/postgresql.conf.sample

src/bin/psql/tab-complete.c

src/include/utils/elog.h

src/include/utils/guc.h