close dangling autoDiscovery goroutine in consumer

[zzzming]

Motivation

The goroutine for auto discovery partitions has never been closed even when consumer is Close()
https://github.com/apache/pulsar-client-go/blob/v0.3.0/pulsar/consumer_impl.go#L236

Currently consumer Close() will stop() the ticker, however, Stop() does not close the ticker's channel. The behaviour is described at https://golang.org/pkg/time/#Ticker.Stop

This bug can leave a large number of dangling goroutines, that results in high CPU consumption.

Modifications

The fix is to introduce a signal channel to send a signal to terminate the partition auto discovery goroutine upon consumer Close().

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? (not applicable)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a followup issue for adding the documentation