cloud_io: add missing error handling to remote::download_object

The call to `drain_response_stream` may throw various transport related
errors (see one example below of a Broken Pipe error observed in CI).
These errors should be handled inside the `remote::download_object`
method because the caller's expectation is that download-related errors
are communicated via the `download_result` return type rather than
through an exception. Some of these errors (like the broken pipe error
below) could also be retried, whereas with the previous implementation
they were not retried.

These exceptions are often ignored by the caller and may be printed as
"Exceptional future ignored" log lines, which cause CI failures and are
less useful for debugging.

The below is an example of one such ignored exceptional future in the
remote partition finalizing background fibre:
```
INFO  2024-10-29 12:41:17,708 [shard 1:main] cloud_storage - [fiber474 kafka/fuzzy-operator-6356-dzxvff/4] - remote_partition.cc:1406 - Finalizing remote storage state...
DEBUG 2024-10-29 12:41:17,723 [shard 1:main] cloud_io - [fiber819~0|1|19984ms] - remote.cc:430 - Receive OK response from "37836c6f-30b0-482f-bb4e-0f3dffdb5cbe/meta/kafka/fuzzy-operator-6356-dzxvff/1_3447/manifest.bin"
WARN  2024-10-29 12:41:17,723 [shard 1:main] http - /37836c6f-30b0-482f-bb4e-0f3dffdb5cbe/meta/kafka/fuzzy-operator-6356-dzxvff/1_3447/manifest.bin - client.cc:414 - receive error std::__1::system_error (error generic:32, System error during SSL read: [error:FFFFFFFF80000020:system library::Broken pipe]: Broken pipe)
WARN  2024-10-29 12:41:17,723 [shard 1:main] seastar - Exceptional future ignored: std::__1::system_error (error generic:32, System error during SSL read: [error:FFFFFFFF80000020:system library::Broken pipe]: Broken pipe), backtrace: 0xa73be23 0xa392e05 0x360a6b8 0x9352157 0x360a71a 0xa48cc6f 0xa49045c 0xa4e77ca 0xa402f3f /opt/redpanda/lib/libc.so.6+0x961b6 /opt/redpanda/lib/libc.so.6+0x11839b
```

src/v/cloud_io/remote.cc

@@ -428,12 +428,18 @@ remote::download_object(download_request download_request) {
 
         if (resp) {
             vlog(ctxlog.debug, "Receive OK response from {}", path);
-            auto buffer
-              = co_await cloud_storage_clients::util::drain_response_stream(
-                resp.value());
-            download_request.payload.append_fragments(std::move(buffer));
-            transfer_details.on_success();
-            co_return download_result::success;
+            try {
+                auto buffer
+                  = co_await cloud_storage_clients::util::drain_response_stream(
+                    resp.value());
+                download_request.payload.append_fragments(std::move(buffer));
+                transfer_details.on_success();
+                co_return download_result::success;
+            } catch (...) {
+                resp
+                  = cloud_storage_clients::util::handle_client_transport_error(
+                    std::current_exception(), ctxlog);
+            }
         }
 
         lease.client->shutdown();