[all] support contexts

[jayshrivastava]

Is your feature request related to a problem? Please describe.
The library does not take a context/context.

Describe the solution you'd like
I expect clients and producers to take a context argument upon creation and have all goroutines created by the clients and producers take a context as well. This is important for tracing (see https://medium.com/swlh/distributed-tracing-for-go-microservice-with-opentracing-1fc1aec76b3e). The context needs to be piped into all goroutines for observability.

It's also important to select on ctx.Done() when sending or recieving to channels. The libary does not do that at the moment. Ex.
What if the command chan is full and cp cannot be send? This method will block. It would be beneficial to also select on a context provided by the user of the library in case the caller wants to cancel long running blocked operations.

pulsar-client-go/pulsar/producer_partition.go

Lines 1462 to 1473 in f476814

	func (p *partitionProducer) Close() {
	if p.getProducerState() != producerReady {
	// Producer is closing
	return
	}
	cp := &closeProducer{doneCh: make(chan struct{})}
	p.cmdChan <- cp
	// wait for close producer request to complete
	<-cp.doneCh
	}

[merlimat]

@jayshrivastava Yes, you're right, it would be really good to take those contexts (and use them).

The main difficulty, as in #1165, is how to do that without breaking compatibility.

Or maybe, it would be a good opportunity to break compatibility, and change versioning scheme to 1.0. Would you like to drive a discussion on the dev@pulsar.apache.org mailing list about this?