Extract upload_component() from backup_task_impl::do_backup() to improve
readability and prepare for optional post-upload cleanup. This refactoring
simplifies the main backup flow by isolating the upload logic into its own
function.
The change is motivated by an upcoming feature that will allow optional
deletion of components after successful upload, which would otherwise add
complexity to do_backup().
Refs scylladb/scylladb#21799
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
32d22371b9