Add `abort_source` to the `get_units` call for the memory semaphore
in the S3 client, allowing the acquisition process to be aborted.
Fixes: https://github.com/scylladb/scylladb/issues/25454
Closes scylladb/scylladb#25469
(cherry picked from commit 380c73ca03)
Closes scylladb/scylladb#25499