[improve][broker] Write the child ownership to ServiceUnitStateChannel instead of ZK when handling bundle split

[Demogorgon314]

Master Issue: apache#16691

Motivation

When the channel handles the split event, we should write the split bundle to zookeeper instead of ServiceUnitStateChannel, since we are using the ServiceUnitStateChannel to store the bundle ownership.

Modifications

• Write the child ownership to ServiceUnitStateChannel instead of ZK when handling bundle split.
• Add unit test to cover this change.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

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

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

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
• Anything that affects deployment

Documentation

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

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