EX-9858 osd: add @read param to dt_write_prep()

EX-9858 osd: add @read param to dt_write_prep()

the purpose is to skip full page reading when OSD is aked for
pages to be written later. in CSDC we need all data as the
pages can be compressed and we may need to decompress them
first.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I2ea9888a1dab419275dbee97e9acc661101b5262
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/55250
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>