Improve configuration for producer and consumer regarding bytes

[saraiva132]

At the moment both producer and consumer configuration parses anything related to size such as:

• batch size
• fetchMinBytes
• fetchMaxBytes

as an integer.

It would be nice to support a better format, something like:

https://github.com/lightbend/config/blob/master/HOCON.md#size-in-bytes-format

[t3hnar]

PRs are welcomed :)