test/backup: Reduce s3 logging from trace to debug

Change s3 log level from TRACE to DEBUG in backup tests.

TRACE level generates excessive log volume with too much low-level
detail about S3 operations. While it was usefult in the early days
of S3 client, nowadays DEBUG level likely provides sufficient
diagnostic information for backup test troubleshooting.

The reduced log volume significantly improves test performance, which
is the main outcome of this change:
- Less I/O time writing logs during test execution
- Faster teardown: each test scans all server logs for errors, and
  smaller logs mean faster grep operations (23.3s → 9.97s for 8-node
  cluster teardown)

Impact on test_restore_with_streaming_scopes[topology4] (8 nodes):
- Log volume: 49 MB → 23 MB (reduced by half)
- Test runtime: 82.55s → 57.53s (30% faster)
- Teardown time: 23.3s → 9.97s (57% faster)

Tests that start smaller clusters also have notable timing improvements

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Closes scylladb/scylladb#30109

test/cluster/object_store/test_backup.py

@@ -471,7 +471,7 @@ async def create_cluster(topology, manager, logger, object_storage=None):
         objconf = object_storage.create_endpoint_conf()
         cfg['object_storage_endpoints'] = objconf
 
-    cmd = [ '--logger-log-level', 'sstables_loader=debug:sstable_directory=trace:snapshots=trace:s3=trace:sstable=debug:http=debug:api=info' ]
+    cmd = [ '--logger-log-level', 'sstables_loader=debug:sstable_directory=trace:snapshots=trace:s3=debug:sstable=debug:http=debug:api=info' ]
     servers = []
     host_ids = {}