Expose MaxOpenRequests parameter for kafka output to increase throughput

[flexitrev]

Background

The number of allowed in flight messages for the C/C++ kafka client is much higher (1,000,000) than the go implementation (5). By exposing the MaxOpenRequests parameter, we would give users more control over throughput settings based on available resources.

https://pkg.go.dev/github.com/ibm/sarama#Config

Enhancement Request

Expose the MaxOpenRequests to let users specify their own value

Documentation Requirements

Basic benchmarking, the impact of changes to this setting and recommendations based on common architectures

[botelastic]

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