pgsql: postgres_fdw: Rename option "restore_stats" to "import_stats".

postgres_fdw: Rename option "restore_stats" to "import_stats".

The option added by commit 28972b6fc was named "restore_stats", because
it was calling pg_restore_relation_stats()/pg_restore_attribute_stats()
in place of fetching a remote rowsample. However, those code paths have
been replaced with calls to
import_relation_statistics()/import_attribute_statistics() (cf. commit
54cd6fc83), so the option is now slightly misnamed.

Switch the option to "import_stats", which more closely reflects both
the functions being called internally, and the user's perception of what
the operation is doing.

Back-patch to v19 where commit 28972b6fc went in.

Suggested-by: Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com>
Author: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Discussion: https://postgr.es/m/CADkLM%3DezuspTk3VD-2EM6XtFP-Dfz7cJKtnbn0cB6gocsAgu1g%40mail.gmail.com
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/48965e14655a007c1250dbd4a1aba65e478ce929

Modified Files
--------------
contrib/postgres_fdw/expected/postgres_fdw.out | 6 +++---
contrib/postgres_fdw/option.c | 8 ++++----
contrib/postgres_fdw/postgres_fdw.c | 16 ++++++++--------
contrib/postgres_fdw/sql/postgres_fdw.sql | 6 +++---
doc/src/sgml/postgres-fdw.sgml | 6 +++---
5 files changed, 21 insertions(+), 21 deletions(-)