[improve][broker] make get topic hash positions async

[leizhiyuan]

merge after #15886

(If this PR fixes a github issue, please add Fixes #<xyz>.)

Fixes #15043

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This change is a trivial rework / code cleanup without any test coverage.

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• Added integration tests for end-to-end deployment with large payloads (10MB)
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[github-actions]

@leizhiyuan:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[github-actions]

@leizhiyuan:Thanks for providing doc info!

[github-actions]

The pr had no activity for 30 days, mark with Stale label.

[gaozhangmin]

This change doesn't match the PR description. some commits is duplicate with #15886

[leizhiyuan]

#16411 has been merged