feat: add 'live_connections' field in the /nodes API

[terry-xiaoyu]

Fixes

Summary

🤖 Generated by Copilot at ab376fa

Incremented the version number of emqx_management and added a new field live_connections to the /api/v4/nodes endpoint. These changes are part of the release preparation for EMQX 4.4.15, which enhances the management and monitoring of EMQX clusters.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

Checklist for CI (.github/workflows) changes

• If changed package build workflow, pass this action (manual trigger)
• Change log has been added to changes/ dir for user-facing artifacts update

[coveralls]

Pull Request Test Coverage Report for Build 5113416231

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 16 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.02%) to 74.927%

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Files with Coverage Reduction	New Missed Lines	%
src/emqx_cm.erl	1	84.85%
src/emqx_broker.erl	2	83.23%
apps/emqx_auth_mongo/src/emqx_auth_mongo.erl	4	95.74%
src/emqx_reason_codes.erl	9	91.43%

Totals
Change from base Build 5111570722:	-0.02%
Covered Lines:	14885
Relevant Lines:	19866

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💛 - Coveralls