As of today, user has to specify `--input-topic` in the stream reset to be able to reset offset to a specific position. For a stream job with multiple external topics that needs to be purged, users usually don't want to name all the topics in order to reset the offsets. It's really painful to look through the entire topology to make sure we purge all the committed offsets.
We could add a config `--reset-all-external-topics` to the reset tool such that when enabled, we could delete offsets for all involved topics. The topic metadata could be acquired by issuing a `DescribeGroup` request from admin client, which is stored in the member subscription information.