ISSUE-16416: The pulsar-admin doesn't set SNI properly when tlsEnableHostnameVerification is false

[sijie]

Original Issue: apache#16416

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Describe the bug
The async-http-client used in pulsar-admin doesn't set SNI properly when tlsEnableHostnameVerification is false, see https://github.com/AsyncHttpClient/async-http-client/blob/master/client/src/main/java/org/asynchttpclient/netty/ssl/DefaultSslEngineFactory.java#L65. This will fail https requests that rely on SNI routing, like a pulsar cluster deployed behind an istio gateway.

The behavior was introduced in the PR apache#15824 since the async-http-client doesn't split the flag for SNI header and hostname verification. @michaeljmarshall

To Reproduce

Set tlsEnableHostnameVerification to false in the client.conf, and use pulsar-admin to operate a pulsar cluster behind the istio gateway.

Expected behavior

The pulsar-admin should set the SNI header properly.

Screenshots
N/A

Desktop (please complete the following information):

• OS: MAC OS X

Additional context