[docs] Add docs for "Dispatch batch messages according consumer permits"

[Jennifer88huang-zz]

Is your feature request related to a problem? Please describe.
In #7266, @rdhabalia improves dispatching of batch messages.

Describe the solution you'd like
When the feature completes, add related docs to this feature.

[codelipenghui]

@jennifer88huang Seems we don't need to add a document for #7266 Since the PR does not introduce any new features and configurations, so I will close it first, feel free to reopen it if needed.

[Jennifer88huang-zz]

@codelipenghui sure, thank you.