[fix][broker] Fix getPartitionedStats miss subscription's messageAckRate

[wangjialing218]

Motivation

Use bin/pulsar-admin topics partitioned-stats get partitioned topic stats, subscription's messageAckRate always be 0.

Modifications

Fix the aggregation logic of subscription stats.
According to the code, chunkedMessageRate has same issue.

Verifying this change

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

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[github-actions]

@wangjialing218 Please add the following content to your PR description and select a checkbox:

- [ ] `doc` <!-- Your PR contains doc changes -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->

[poorbarcode]

Could you write a test?

[poorbarcode]

Since we will start the RC version of 3.0.0 on 2023-04-11, I will change the label/milestone of PR who have not been merged.

• The PR of type feature is deferred to 3.1.0
• The PR of type fix is deferred to 3.0.1

So drag this PR to 3.0.1