rgw: align object chunk size with pool alignment

Fixes: #8442
Backport: firefly
Data pools might have strict write alignment requirements. Use pool
alignment info when setting the max_chunk_size for the write.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
rgw: object write should not exceed part size

Fixes: #8928

This can happen if the stripe size is not a multiple of the chunk size.

Backport: firefly

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>