[Improve][broker] Improve replicatorDispacherRate endpoint to pure async.

[mattisonchao]

Motivation

Since Pulsar is a fully asynchronous project, we need to avoid using thread-blocking methods.

Also, we can see #14365

Modifications

• Improve replicatorDispacherRate relative endpoint to pure async.

Verifying this change

• Make sure that the change passes the CI checks.

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• Anything that affects deployment: (yes / no / don't know)

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