out_rdkafka2: enable idempotency for kafka producers

[dipendra-singh]

Which issue(s) this PR fixes:
None.

What this PR does / why we need it:
In order to enable Idempotency for kafka producers, rdkafka allowes us to enable this. (here)

Docs Changes:
README.md : Added to usage template for better visibility.

Release Note:
Same as the title.

[ashie]

Any rdkafka options can be set by rdkafka_options parameter.
e.g.)

<match tag>
  @type rdkafka2
   rdkafka_options {                                                                                                                                        
     "enable.idempotence" : true
   }
   ....
</match>

Is there any reason to add a new specific parameter for idempotence?

[dipendra-singh]

@ashie To keep the consistency between this and other plugins. One needs to explore rdkafka options to have similar features to that of other plugins.

[ashie]

Ah, I see. Thanks for clarification.
It seems reasonable.

fluent-plugin-kafka/lib/fluent/plugin/out_kafka2.rb

Line 37 in ea0f10a

config_param :idempotent, :bool, :default => false, :desc => 'Enable idempotent producer'

[dipendra-singh]

hey @ashie
Can we close this?