DLPX-87575 agent panic: request has timed out (openzfs#1160)

When restarting the agent, it uses ListObjects operations to find any objects
that are part of the in-progress TXG.  If there are a large number of these
objects, this may take a while, resulting in the following agent panic:

```
thread 'zoa' panicked at 'called `Result::unwrap()` on an `Err` value: request has timed out

Caused by:
    operation attempt timeout (single attempt) occurred after 2s', zettaobject/src/object_access/mod.rs:491:42
stack backtrace:
...
      zettaobject::object_access::ObjectAccess::try_list_after::{{closure}}
             at zfs/cmd/zfs_object_agent/zettaobject/src/object_access/mod.rs:491:35
...
   8: zettaobject::pool::recover_list::{{closure}}::{{closure}}::{{closure}}
             at zfs/cmd/zfs_object_agent/zettaobject/src/pool.rs:1928:17
```

The problem is that we configure the “retrying” client of the AWS SDK to have a
2 second timeout.  (This “retrying” client is only used for ListObjects
requests.) After this timeout expires, the SDK returns an error.  However, in
this case the request may reasonably take longer, and we want to keep waiting.

The fix is to not configure a timeout on the “retrying” client.

cmd/zfs_object_agent/zettaobject/src/object_access/s3.rs

@@ -204,11 +204,6 @@ impl S3ObjectAccess {
                     .with_max_attempts(u32::MAX)
                     .with_initial_backoff(Duration::from_millis(100)),
             )
-            .timeout_config(
-                TimeoutConfig::builder()
-                    .operation_attempt_timeout(*PER_REQUEST_TIMEOUT)
-                    .build(),
-            )
             .load()
             .await;
         // Force path style URLs, which are required for on-prem object stores.