ISSUE-14304: CommandLookupTopic.advertisedListenerName may be blank

[sijie]

Original Issue: apache#14304

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Describe the bug
Some of the language bindings supply an empty string for the advertisedListenerName field of CommandLookupTopic (e.g. Java vs Golang). This confuses the broker, who then fails to apply the default advertised listener for the given server port. This, in turn, leads to an incorrect topic lookup response and a subsequent connection failure.

For background, see [PIP 95] Smart Listener Selection with Multiple Bind Addresses.

To Reproduce
Steps to reproduce the behavior:

1. Configure a broker with a bind address that is associated with an advertised listener.
2. Using various language clients, send a topic lookup request without an explicit advertised listener to the bind address. Expect the default advertised listener for that binding to be used.
3. Observe that some clients receive the correct advertised listener, others don't.

Expected behavior
Expect the binding-specific advertised listener to be automatically applied to lookup request.

Proposed Solution
Enhance the broker to check for an empty string in the advertisedListenerName field. (code)

[EronWright]

Reopening to track cherry-picking to 2.9.