feat: change streams.Task interface and update to v7

[Skandalik]

Changes made here:

• task.OnError now accepts function signature func(error) error, allowing to handle errors throughout the stream better than before.
  • By default error is returned further and task is stopped
  • It's up to developer's decision to stop the task, depending on the type of error for example. Task is going to be stopped only if error is returned from OnError.
• updated Shopify/sarama to IBM/sarama with kafka tests updates
• removed cache package as it had deprecated pkg/v4 as dependency, currently there's we have no time to reimplement cache sink, therefore it's removed in v7
• removed sql package as it had data race related with database/sql usage. Hopefully we will be able to bring it back in the future.
• removed xerrors dependency
• general dependencies update
• fixed data race in kafka sink related with errors

[mkocztorz]

One thing I see here is Unlock function call is now optional but I guess its intended. The other difference is the p.errFn is now called before p.Unlock. Good, as long as you know its ok.

[Skandalik]

Yeah, previously p.Unlock has been called before errFn, but we were always stopping the task. Currently task is supposed to continue running until you return an error from errFn.