vfs: Add VFS_OPEN_HOW_WITH_BACKUP_INTENT

vfs: Add VFS_OPEN_HOW_WITH_BACKUP_INTENT

Indicate BACKUP_INTENT to vfs_openat(). Why? I have a customer request
who wants to add O_NOATIME in this case to avoid metadata updates when
a backup or virus-checking application comes along.

This does not fully handle BACKUP_INTENT correctly, this would require
become_root() appropriately. We might want to do that later after a
lot of careful security audit, but this patch independently might
already provide some infrastructure for it.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Thu Oct  5 14:00:33 UTC 2023 on atb-devel-224