feat: add functionality pause and resume for consumer

[Abdulsametileri]

Based on this issue and some internal projects, I implemented a pause/resume consuming mechanism.

Before implementation, I researched segmentio/kafka-go issues for this functionality. I came across this issue. achille-roussel answer is really clear. If I stop calling FetchMessage, the consumer pauses. If I invoke FetchMessage, it resumes. Consumer group is still Stable because when I called kafka.NewConsumer, segmentio creates a goroutine and starts heartbeat to the broker under the hood!

First, I defined two methods, Resume and Pause on the Consumer interface. So our clients can invoke this easily. You can refer to examples/with-pause-resume-consumer/main.go. It basically

consumer, _ := kafka.NewConsumer(consumerCfg)
defer consumer.Stop()

consumer.Consume()
fmt.Println("Consumer started...!")

go func() {
  time.Sleep(10 * time.Second)
  consumer.Pause()
  
  time.Sleep(10 * time.Second)
  consumer.Resume()
  
  time.Sleep(10 * time.Second)
  consumer.Pause()
  
  time.Sleep(10 * time.Second)
  consumer.Resume()
  
  time.Sleep(10 * time.Second)
  consumer.Pause()
}()

I also added related documentation within the example.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (4f33fc4) 35.62% compared to head (9565659) 37.07%.

Files	Patch %	Lines
consumer_base.go	54.54%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v2      #89      +/-   ##
==========================================
+ Coverage   35.62%   37.07%   +1.45%     
==========================================
  Files          19       19              
  Lines         685      712      +27     
==========================================
+ Hits          244      264      +20     
- Misses        434      441       +7     
  Partials        7        7              

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[mhmtszr]

LGTM.