I can request the current list of topics and partitions from the system partition leader

[ThorbenLindhauer]

This is different to requesting the cluster topology in that it includes all the partitions that should be currently available, regardless whether they are known to the broker receiving the request. The tradeoff is that this request will only work if the system partition leader is reachable.

The response should contain a list of all partitions and to which topic they belong. This allows users to inspect which topics should be there with how many partitions.

[ThorbenLindhauer]

@jsam, here's how the request works:

• send a control message request of type REQUEST_PARTITIONS to the leader of the system partition (see https://github.com/zeebe-io/zb-protocol/commit/de12b7c60426ba45d6a21490df4caf60a605ee1f)
• request body (i.e. field data) can be empty
• control message response contains msgpack-encoded JSON as follows:

{
  "partitions": [
    {"id": 1,
     "topic": "foo"},
    ...
  ]
}

The system topic is currently not included in the response.

[ThorbenLindhauer]

Follow-up issue: #577