pgsql: Add file_extend_method=posix_fallocate,write_zeros.

Add file_extend_method=posix_fallocate,write_zeros.

Provide a way to disable the use of posix_fallocate() for relation
files. It was introduced by commit 4d330a61bb1. The new setting
file_extend_method=write_zeros can be used as a workaround for problems
reported from the field:

* BTRFS compression is disabled by the use of posix_fallocate()
* XFS could produce spurious ENOSPC errors in some Linux kernel
versions, though that problem is reported to have been fixed

The default is file_extend_method=posix_fallocate if available, as
before. The write_zeros option is similar to PostgreSQL < 16, except
that now it's multi-block.

Backpatch-through: 16
Reviewed-by: Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com>
Reported-by: Dimitrios Apostolou <jimis(at)gmx(dot)net>
Discussion: https://postgr.es/m/b1843124-fd22-e279-a31f-252dffb6fbf2%40gmx.net

Branch
------
REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e37b598028469d260650e5e1671c8275d30e22b6

Modified Files
--------------
doc/src/sgml/config.sgml | 36 +++++++++++++++++++++++++++
src/backend/storage/file/fd.c | 3 +++
src/backend/storage/smgr/md.c | 21 ++++++++++++----
src/backend/utils/misc/guc_tables.c | 19 ++++++++++++++
src/backend/utils/misc/postgresql.conf.sample | 5 ++++
src/include/storage/fd.h | 11 ++++++++
6 files changed, 90 insertions(+), 5 deletions(-)