avoid create new subscription name for reader if it's already configed

[aloyszhang]

Motivation

For a reader, pulsar will create a new subscription name first without checking whether it's existed or not.

 String subscription = "multiTopicsReader-" + DigestUtils.sha1Hex(UUID.randomUUID().toString()).substring(0, 10);
        if (StringUtils.isNotBlank(readerConfiguration.getSubscriptionRolePrefix())) {
            subscription = readerConfiguration.getSubscriptionRolePrefix() + "-" + subscription;
        }
if (StringUtils.isNotBlank(readerConfiguration.getSubscriptionName())) {
            subscription = readerConfiguration.getSubscriptionName();
        }

This pull request aims to avoid create a new subscription name for reader if it's already set before.

Modifications

Check subscription from the ReaderConfigurationData first and if already exist, we do not need to create a subscription name.

Verifying this change

This change is a trivial rework 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)
• The rest endpoints: ( no)
• The admin cli options: ( no)
• Anything that affects deployment: ( now)

Documentation

no document need be added or updated since this change has nothing to do with API and configuration

[aloyszhang]

/pulsarbot run-failure-checks

[eolivelli]

Lgtm