Store event data and metadata as JSON

[slashdotdash]

Issue originally raised in Commanded by @drozzy (#81).

Need to investigate whether it is possible to persist event data & metadata as JSON when using a JSON event serializer.

Example

Persisted events from Event Store:

{
    "correlationId": "ccf88746-06ba-459f-b93a-9ccce1cebdf1",
    "readerPosition": {
        "$s": {
            "$ce-account": 6
        }
    },
    "events": [
        {
            "eventStreamId": "account-333-121-568-3245",
            "eventType": "Elixir.Bank.Events.AccountOpened",
            "data": "{\"timestamp_utc\":1506096118,\"initial_balance\":0,\"client_id\":\"3324-john.oliver\",\"account_id\":\"333-121-568-3245\"}",
            "metadata": "{\"$correlationId\":\"7e083e9e-bcf6-4cc5-8cc8-47d84f14ec50\"}",
            "readerPosition": {
                "$s": {
                    "$ce-account": 0
                }
            }
        },
   ]
}

Possible solution

Set the data_content_type and metadata_content_type to 1 for Extreme's ExMsg.NewEvent message (source).

[drozzy]

It would be nice if these were parameters we could set ourselves, and not hard-corded (to 0 or 1).

[drozzy]

Parameter for possibly to write_events, but I don't know where that is being called.
It should probably be set in the config:

config :commanded_extreme_adapter,
  serializer: Commanded.Serialization.JsonSerializer,
  stream_prefix: "commandeddev"
  data_content_type: 1

Or, per stream (somehow).