modify from s3 to object storage

modules/reference/pages/rpk/rpk-cluster/rpk-cluster-self-test-start.adoc

@@ -17,10 +17,10 @@ Available tests to run:
 * *Cloud tests*
 ** Latency test: 1024-bit object.
 ** Depending on cluster read/write permissions (xref:reference:properties/object-storage-properties.adoc#cloud_storage_enable_remote_read[`cloud_storage_enable_remote_read`], xref:reference:properties/object-storage-properties.adoc#cloud_storage_enable_remote_write[`cloud_storage_enable_remote_write`]), a series of cloud storage operations are performed:
-*** Upload an object to an S3 bucket.
-*** List objects in the bucket.
-*** Download an object from the bucket.
-*** Delete the original object from the bucket, if it was uploaded.
+*** Upload an object to an object storage.
+*** List objects in the object storage.
+*** Download an object from the object storage.
+*** Delete the original object from the object storage, if it was uploaded.
 
 This command immediately returns on success, and the tests run asynchronously. The
 user polls for results with the xref:./rpk-cluster-self-test-status.adoc[rpk cluster self-test status]