before this change, we use the default options for
performing read on the input. and the default options
is like
```c++
struct file_input_stream_options {
size_t buffer_size = 8192; ///< I/O buffer size
unsigned read_ahead = 0; ///< Maximum number of extra read-ahead operations
};
```
which is not able to offer good throughput when
reading from disk, when we stream to S3.
so, in this change, we use options which allows better throughput.
Refs 061def001d
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#20074
a78f46aad7