Make PartitionsAutoDiscoveryInterval configurable

[hunter2046]

Motivation

partitionsAutoDiscoveryInterval is currently hardcoded to 1 minute:

pulsar-client-go/pulsar/producer_impl.go

Line 60 in 6ab17dc

var partitionsAutoDiscoveryInterval = 1 * time.Minute

I could think of two reasons for making it a configurable value:

• A faster or slower partitions discovery is desired. A faster one is more likely when users would like a partition increment to be effective more quickly.
• Allow a test to be able to set it to a much smaller time duration so that the test could exercise the logic within a reasonable short time

Modifications

Added PartitionsAutoDiscoveryInterval into ProducerOptions with a default value of 1 minute.

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): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / GoDocs / not documented)
• 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

[cckellogg]

What happens if a negative value is passed in?

[hunter2046]

Thanks for the catch. Updated the check to include negative values.