Channel consumer and batch producers ignore configured batch sizes internally

[EVODelavega]

When using a channel-based consumer, the size of the event channel is configurable. However, the internal consumeReader function passes the maxEvents parameter as a hard-coded 1000 (the default config).

Same goes for batch producers: the batch/channel size can be specified through the ConfigMap parameter, but the channelBatchProducer relies on a const batchSize int = 100000 (again, the default batch size).

I've opened a PR to have the maxEvents and batchSize depend on the config and/or the actual space available in the channel:

#17