[improve][broker] Expose topic fence related information in stats command

[lifepuzzlefun]

Motivation

Current if topic in fenced stats the write io path will hang for some time. we need tool to check fence status.

Modifications

1. record topic chang to fenced timestamp.
2. expose fence, fence time, and pendingAddEntry information in topic stats.

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
• The metrics
• Anything that affects deployment

Documentation

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

Matching PR in forked repository

PR in forked repository:

[Technoboy-]

Please also add a test

[RobertIndie]

I think we need a PIP for this change.

https://github.com/apache/pulsar/tree/master/pip#when-is-a-pip-required
It involves changes to topic stats.

[github-actions]

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