Make broker connection retry interval configurable in kafka sarama input

[cll-gg]

When the sarama loses its connection with the broker, it retries to establish it.
By default, the interval for retrying is set to 250ms (see here).

What we occasionally observe is that when a kafka cluster instance restarts, there's a thundering herd of benthos consumers retrying the connection. If we make the interval configurable, we can improve this situation.

I'm also open to making a PR to make the whole sarama retry config configurable, made a draft PR for that here, but maybe that's overkill.

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